dotemacs

transient.info (110227B)

---

 This is transient.info, produced by makeinfo version 6.7 from
 transient.texi.
 
      Copyright (C) 2018-2021 Jonas Bernoulli <jonas@bernoul.li>
 
      You can redistribute this document and/or modify it under the terms
      of the GNU General Public License as published by the Free Software
      Foundation, either version 3 of the License, or (at your option)
      any later version.
 
      This document is distributed in the hope that it will be useful,
      but WITHOUT ANY WARRANTY; without even the implied warranty of
      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      General Public License for more details.
 
 INFO-DIR-SECTION Emacs
 START-INFO-DIR-ENTRY
 * Transient: (transient). Transient Commands.
 END-INFO-DIR-ENTRY
 
 
 File: transient.info,  Node: Top,  Next: Introduction,  Up: (dir)
 
 Transient User and Developer Manual
 ***********************************
 
 Taking inspiration from prefix keys and prefix arguments, Transient
 implements a similar abstraction involving a prefix command, infix
 arguments and suffix commands.  We could call this abstraction a
 "transient command", but because it always involves at least two
 commands (a prefix and a suffix) we prefer to call it just a
 "transient".
 
    When the user calls a transient prefix command, then a transient
 (temporary) keymap is activated, which binds the transient’s infix and
 suffix commands, and functions that control the transient state are
 added to ‘pre-command-hook’ and ‘post-command-hook’.  The available
 suffix and infix commands and their state are shown in a popup buffer
 until the transient is exited by invoking a suffix command.
 
    Calling an infix command causes its value to be changed, possibly by
 reading a new value in the minibuffer.
 
    Calling a suffix command usually causes the transient to be exited
 but suffix commands can also be configured to not exit the transient.
 
 This manual is for Transient version 0.3.7.
 
      Copyright (C) 2018-2021 Jonas Bernoulli <jonas@bernoul.li>
 
      You can redistribute this document and/or modify it under the terms
      of the GNU General Public License as published by the Free Software
      Foundation, either version 3 of the License, or (at your option)
      any later version.
 
      This document is distributed in the hope that it will be useful,
      but WITHOUT ANY WARRANTY; without even the implied warranty of
      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      General Public License for more details.
 
 * Menu:
 
 * Introduction::
 * Usage::
 * Modifying Existing Transients::
 * Defining New Commands::
 * Classes and Methods::
 * Related Abstractions and Packages::
 * FAQ::
 * Keystroke Index::
 * Command Index::
 * Function Index::
 * Variable Index::
 
 — The Detailed Node Listing —
 
 Usage
 
 * Invoking Transients::
 * Aborting and Resuming Transients::
 * Common Suffix Commands::
 * Saving Values::
 * Using History::
 * Getting Help for Suffix Commands::
 * Enabling and Disabling Suffixes::
 * Other Commands::
 * Other Options::
 
 Defining New Commands
 
 * Defining Transients::
 * Binding Suffix and Infix Commands::
 * Defining Suffix and Infix Commands::
 * Using Infix Arguments::
 * Transient State::
 
 Binding Suffix and Infix Commands
 
 * Group Specifications::
 * Suffix Specifications::
 
 
 Classes and Methods
 
 * Group Classes::
 * Group Methods::
 * Prefix Classes::
 * Suffix Classes::
 * Suffix Methods::
 * Prefix Slots::
 * Suffix Slots::
 * Predicate Slots::
 
 Suffix Methods
 
 * Suffix Value Methods::
 * Suffix Format Methods::
 
 
 Related Abstractions and Packages
 
 * Comparison With Prefix Keys and Prefix Arguments::
 * Comparison With Other Packages::
 
 
 
 File: transient.info,  Node: Introduction,  Next: Usage,  Prev: Top,  Up: Top
 
 1 Introduction
 **************
 
 Taking inspiration from prefix keys and prefix arguments, Transient
 implements a similar abstraction involving a prefix command, infix
 arguments and suffix commands.  We could call this abstraction a
 "transient command", but because it always involves at least two
 commands (a prefix and a suffix) we prefer to call it just a
 "transient".
 
      Transient keymaps are a feature provided by Emacs.  Transients as
      implemented by this package involve the use of transient keymaps.
 
      Emacs provides a feature that it calls "prefix commands".  When we
      talk about "prefix commands" in this manual, then we mean our own
      kind of "prefix commands", unless specified otherwise.  To avoid
      ambiguity we sometimes use the terms "transient prefix command" for
      our kind and "regular prefix command" for Emacs’ kind.
 
    When the user calls a transient prefix command, then a transient
 (temporary) keymap is activated, which binds the transient’s infix and
 suffix commands, and functions that control the transient state are
 added to ‘pre-command-hook’ and ‘post-command-hook’.  The available
 suffix and infix commands and their state are shown in a popup buffer
 until the transient state is exited by invoking a suffix command.
 
    Calling an infix command causes its value to be changed.  How that is
 done depends on the type of the infix command.  The simplest case is an
 infix command that represents a command-line argument that does not take
 a value.  Invoking such an infix command causes the switch to be toggled
 on or off.  More complex infix commands may read a value from the user,
 using the minibuffer.
 
    Calling a suffix command usually causes the transient to be exited;
 the transient keymaps and hook functions are removed, the popup buffer
 no longer shows information about the (no longer bound) suffix commands,
 the values of some public global variables are set, while some internal
 global variables are unset, and finally the command is actually called.
 Suffix commands can also be configured to not exit the transient.
 
    A suffix command can, but does not have to, use the infix arguments
 in much the same way any command can choose to use or ignore the prefix
 arguments.  For a suffix command that was invoked from a transient the
 variable ‘transient-current-suffixes’ and the function ‘transient-args’
 serve about the same purpose as the variables ‘prefix-arg’ and
 ‘current-prefix-arg’ do for any command that was called after the prefix
 arguments have been set using a command such as ‘universal-argument’.
 
    The information shown in the popup buffer while a transient is active
 looks a bit like this:
 
      ,-----------------------------------------
      |Arguments
      | -f Force (--force)
      | -a Annotate (--annotate)
      |
      |Create
      | t tag
      | r release
      `-----------------------------------------
 
      This is a simplified version of ‘magit-tag’.  Info manuals do not
      support images or colored text, so the above "screenshot" lacks
      some information; in practice you would be able to tell whether the
      arguments ‘--force’ and ‘--annotate’ are enabled or not based on
      their color.
 
    Transient can be used to implement simple "command dispatchers".  The
 main benefit then is that the user can see all the available commands in
 a popup buffer.  That is useful by itself because it frees the user from
 having to remember all the keys that are valid after a certain prefix
 key or command.  Magit’s ‘magit-dispatch’ (on ‘C-x M-g’) command is an
 example of using Transient to merely implement a command dispatcher.
 
    In addition to that, Transient also allows users to interactively
 pass arguments to commands.  These arguments can be much more complex
 than what is reasonable when using prefix arguments.  There is a limit
 to how many aspects of a command can be controlled using prefix
 arguments.  Furthermore what a certain prefix argument means for
 different commands can be completely different, and users have to read
 documentation to learn and then commit to memory what a certain prefix
 argument means to a certain command.
 
    Transient suffix commands on the other hand can accept dozens of
 different arguments without the user having to remember anything.  When
 using Transient, then one can call a command with arguments that are
 just as complex as when calling the same function non-interactively
 using code.
 
    Invoking a transient command with arguments is similar to invoking a
 command in a shell with command-line completion and history enabled.
 One benefit of the Transient interface is that it remembers history not
 only on a global level ("this command was invoked using these arguments
 and previously it was invoked using those other arguments"), but also
 remembers the values of individual arguments independently.  See *note
 Using History::.
 
    After a transient prefix command is invoked ‘C-h <key>’ can be used
 to show the documentation for the infix or suffix command that ‘<key>’
 is bound to (see *note Getting Help for Suffix Commands::) and infixes
 and suffixes can be removed from the transient using ‘C-x l <key>’.
 Infixes and suffixes that are disabled by default can be enabled the
 same way.  See *note Enabling and Disabling Suffixes::.
 
    Transient ships with support for a few different types of specialized
 infix commands.  A command that sets a command line option for example
 has different needs than a command that merely toggles a boolean flag.
 Additionally Transient provides abstractions for defining new types,
 which the author of Transient did not anticipate (or didn’t get around
 to implementing yet).
 
 
 File: transient.info,  Node: Usage,  Next: Modifying Existing Transients,  Prev: Introduction,  Up: Top
 
 2 Usage
 *******
 
 * Menu:
 
 * Invoking Transients::
 * Aborting and Resuming Transients::
 * Common Suffix Commands::
 * Saving Values::
 * Using History::
 * Getting Help for Suffix Commands::
 * Enabling and Disabling Suffixes::
 * Other Commands::
 * Other Options::
 
 
 File: transient.info,  Node: Invoking Transients,  Next: Aborting and Resuming Transients,  Up: Usage
 
 2.1 Invoking Transients
 =======================
 
 A transient prefix command is invoked like any other command by pressing
 the key that is bound to that command.  The main difference to other
 commands is that a transient prefix command activates a transient
 keymap, which temporarily binds the transient’s infix and suffix
 commands.  Bindings from other keymaps may, or may not, be disabled
 while the transient state is in effect.
 
    There are two kinds of commands that are available after invoking a
 transient prefix command; infix and suffix commands.  Infix commands set
 some value (which is then shown in a popup buffer), without leaving the
 transient.  Suffix commands on the other hand usually quit the transient
 and they may use the values set by the infix commands, i.e.  the infix
 *arguments*.
 
    Instead of setting arguments to be used by a suffix command, infix
 commands may also set some value by side-effect, e.g.  by setting the
 value of some variable.
 
 
 File: transient.info,  Node: Aborting and Resuming Transients,  Next: Common Suffix Commands,  Prev: Invoking Transients,  Up: Usage
 
 2.2 Aborting and Resuming Transients
 ====================================
 
 To quit the transient without invoking a suffix command press ‘C-g’.
 
    Key bindings in transient keymaps may be longer than a single event.
 After pressing a valid prefix key, all commands whose bindings do not
 begin with that prefix key are temporarily unavailable and grayed out.
 To abort the prefix key press ‘C-g’ (which in this case only quits the
 prefix key, but not the complete transient).
 
    A transient prefix command can be bound as a suffix of another
 transient.  Invoking such a suffix replaces the current transient state
 with a new transient state, i.e.  the available bindings change and the
 information displayed in the popup buffer is updated accordingly.
 Pressing ‘C-g’ while a nested transient is active only quits the
 innermost transient, causing a return to the previous transient.
 
    ‘C-q’ or ‘C-z’ on the other hand always exits all transients.  If you
 use the latter, then you can later resume the stack of transients using
 ‘M-x transient-resume’.
 
 ‘C-g’     (‘transient-quit-seq’)
 ‘C-g’     (‘transient-quit-one’)
 
      This key quits the currently active incomplete key sequence, if
      any, or else the current transient.  When quitting the current
      transient, then it returns to the previous transient, if any.
 
    Transient’s predecessor bound ‘q’ instead of ‘C-g’ to the quit
 command.  To learn how to get that binding back see
 ‘transient-bind-q-to-quit’’s doc string.
 
 ‘C-q’     (‘transient-quit-all’)
 
      This command quits the currently active incomplete key sequence, if
      any, and all transients, including the active transient and all
      suspended transients, if any.
 
 ‘C-z’     (‘transient-suspend’)
 
      Like ‘transient-quit-all’, this command quits an incomplete key
      sequence, if any, and all transients.  Additionally it saves the
      stack of transients so that it can easily be resumed (which is
      particularly useful if you quickly need to do "something else" and
      the stack is deeper than a single transient and/or you have already
      changed the values of some infix arguments).
 
      Note that only a single stack of transients can be saved at a time.
      If another stack is already saved, then saving a new stack discards
      the previous stack.
 
 ‘M-x transient-resume’     (‘transient-resume’)
 
      This command resumes the previously suspended stack of transients,
      if any.
 
 
 File: transient.info,  Node: Common Suffix Commands,  Next: Saving Values,  Prev: Aborting and Resuming Transients,  Up: Usage
 
 2.3 Common Suffix Commands
 ==========================
 
 A few shared suffix commands are available in all transients.  These
 suffix commands are not shown in the popup buffer by default.
 
    This includes the aborting commands mentioned in the previous node as
 well as some other commands that are all bound to ‘C-x <key>’.  After
 ‘C-x’ is pressed, a section featuring all these common commands is
 temporarily shown in the popup buffer.  After invoking one of them, the
 section disappears again.  Note however that one of these commands is
 described as "Show common permanently"; invoke that if you want the
 common commands to always be shown for all transients.
 
 ‘C-x t’     (‘transient-toggle-common’)
 
      This command toggles whether the generic commands that are common
      to all transients are always displayed or only after typing the
      incomplete prefix key sequence ‘C-x’.  This only affects the
      current Emacs session.
 
  -- User Option: transient-show-common-commands
 
      This option controls whether shared suffix commands are shown
      alongside the transient-specific infix and suffix commands.  By
      default the shared commands are not shown to avoid overwhelming the
      user with to many options.
 
      While a transient is active, pressing ‘C-x’ always shows the common
      command.  The value of this option can be changed for the current
      Emacs session by typing ‘C-x t’ while a transient is active.
 
    The other common commands are described in either the previous node
 or in one of the following nodes.
 
    Some of Transient’s key bindings differ from the respective bindings
 of Magit-Popup; see *note FAQ:: for more information.
 
 
 File: transient.info,  Node: Saving Values,  Next: Using History,  Prev: Common Suffix Commands,  Up: Usage
 
 2.4 Saving Values
 =================
 
 After setting the infix arguments in a transient, the user can save
 those arguments for future invocations.
 
    Most transients will start out with the saved arguments when they are
 invoked.  There are a few exceptions though.  Some transients are
 designed so that the value that they use is stored externally as the
 buffer-local value of some variable.  Invoking such a transient again
 uses the buffer-local value.  (1)
 
    If the user does not save the value and just exits using a regular
 suffix command, then the value is merely saved to the transient’s
 history.  That value won’t be used when the transient is next invoked
 but it is easily accessible (see *note Using History::).
 
 ‘C-x s’     (‘transient-set’)
 
      This command saves the value of the active transient for this Emacs
      session.
 
 ‘C-x C-s’     (‘transient-save’)
 
      Save the value of the active transient persistently across Emacs
      sessions.
 
  -- User Option: transient-values-file
 
      This file is used to persist the values of transients between Emacs
      sessions.
 
    ---------- Footnotes ----------
 
    (1) ‘magit-diff’ and ‘magit-log’ are two prominent examples, and
 their handling of buffer-local values is actually a bit more complicated
 than outlined above and even customizable.
 
 
 File: transient.info,  Node: Using History,  Next: Getting Help for Suffix Commands,  Prev: Saving Values,  Up: Usage
 
 2.5 Using History
 =================
 
 Every time the user invokes a suffix command the transient’s current
 value is saved to its history.  These values can be cycled through the
 same way one can cycle through the history of commands that read
 user-input in the minibuffer.
 
 ‘C-M-p’     (‘transient-history-prev’)
 ‘C-x p’     (‘transient-history-prev’)
 
      This command switches to the previous value used for the active
      transient.
 
 ‘C-M-n’     (‘transient-history-next’)
 ‘C-x n’     (‘transient-history-next’)
 
      This command switches to the next value used for the active
      transient.
 
    In addition to the transient-wide history, Transient of course
 supports per-infix history.  When an infix reads user-input using the
 minibuffer, then the user can use the regular minibuffer history
 commands to cycle through previously used values.  Usually the same keys
 as those mentioned above are bound to those commands.
 
    Authors of transients should arrange for different infix commands
 that read the same kind of value to also use the same history key (see
 *note Suffix Slots::).
 
    Both kinds of history are saved to a file when Emacs is exited.
 
  -- User Option: transient-history-file
 
      This file is used to persist the history of transients and their
      infixes between Emacs sessions.
 
  -- User Option: transient-history-limit
 
      This option controls how many history elements are kept at the time
      the history is saved in ‘transient-history-file’.
 
 
 File: transient.info,  Node: Getting Help for Suffix Commands,  Next: Enabling and Disabling Suffixes,  Prev: Using History,  Up: Usage
 
 2.6 Getting Help for Suffix Commands
 ====================================
 
 Transients can have many suffixes and infixes that the user might not be
 familiar with.  To make it trivial to get help for these, Transient
 provides access to the documentation directly from the active transient.
 
 ‘C-h’     (‘transient-help’)
 
      This command enters help mode.  When help mode is active, then
      typing ‘<key>’ shows information about the suffix command that
      ‘<key>’ normally is bound to (instead of invoking it).  Pressing
      ‘C-h’ a second time shows information about the _prefix_ command.
 
      After typing ‘<key>’ the stack of transient states is suspended and
      information about the suffix command is shown instead.  Typing ‘q’
      in the help buffer buries that buffer and resumes the transient
      state.
 
    What sort of documentation is shown depends on how the transient was
 defined.  For infix commands that represent command-line arguments this
 ideally shows the appropriate manpage.  ‘transient-help’ then tries to
 jump to the correct location within that.  Info manuals are also
 supported.  The fallback is to show the command’s doc string, for
 non-infix suffixes this is usually appropriate.
 
 
 File: transient.info,  Node: Enabling and Disabling Suffixes,  Next: Other Commands,  Prev: Getting Help for Suffix Commands,  Up: Usage
 
 2.7 Enabling and Disabling Suffixes
 ===================================
 
 The user base of a package that uses transients can be very diverse.
 This is certainly the case for Magit; some users have been using it and
 Git for a decade, while others are just getting started now.
 
    For that reason a mechanism is needed that authors can use to
 classify a transient’s infixes and suffixes along the
 essentials...everything spectrum.  We use the term "levels" to describe
 that mechanism.
 
    Each suffix command is placed on a level and each transient has a
 level (called transient-level), which controls which suffix commands are
 available.  Integers between 1 and 7 (inclusive) are valid levels.  For
 suffixes, 0 is also valid; it means that the suffix is not displayed at
 any level.
 
    The levels of individual transients and/or their individual suffixes
 can be changed interactively, by invoking the transient and then
 pressing ‘C-x l’ to enter the "edit" mode, see below.
 
    The default level for both transients and their suffixes is 4.  The
 ‘transient-default-level’ option only controls the default for
 transients.  The default suffix level is always 4.  The authors of
 transients should place certain suffixes on a higher level, if they
 expect that it won’t be of use to most users, and they should place very
 important suffixes on a lower level, so that they remain available even
 if the user lowers the transient level.
 
  -- User Option: transient-default-level
 
      This option controls which suffix levels are made available by
      default.  It sets the transient-level for transients for which the
      user has not set that individually.
 
  -- User Option: transient-levels-file
 
      This file is used to persist the levels of transients and their
      suffixes between Emacs sessions.
 
 ‘C-x l’     (‘transient-set-level’)
 
      This command enters edit mode.  When edit mode is active, then all
      infixes and suffixes that are currently usable are displayed along
      with their levels.  The colors of the levels indicate whether they
      are enabled or not.  The level of the transient is also displayed
      along with some usage information.
 
      In edit mode, pressing the key that would usually invoke a certain
      suffix instead prompts the user for the level that suffix should be
      placed on.
 
      Help mode is available in edit mode.
 
      To change the transient level press ‘C-x l’ again.
 
      To exit edit mode press ‘C-g’.
 
      Note that edit mode does not display any suffixes that are not
      currently usable.  ‘magit-rebase’ for example shows different
      suffixes depending on whether a rebase is already in progress or
      not.  The predicates also apply in edit mode.
 
      Therefore, to control which suffixes are available given a certain
      state, you have to make sure that that state is currently active.
 
 
 File: transient.info,  Node: Other Commands,  Next: Other Options,  Prev: Enabling and Disabling Suffixes,  Up: Usage
 
 2.8 Other Commands
 ==================
 
 When invoking a transient in a small frame, the transient window may not
 show the complete buffer, making it necessary to scroll, using the
 following commands.  These commands are never shown in the transient
 window, and the key bindings are the same as for ‘scroll-up-command’ and
 ‘scroll-down-command’ in other buffers.
 
  -- Command: transient-scroll-up arg
 
      This command scrolls text of transient popup window upward ARG
      lines.  If ARG is ‘nil’, then it scrolls near full screen.  This is
      a wrapper around ‘scroll-up-command’ (which see).
 
  -- Command: transient-scroll-down arg
 
      This command scrolls text of transient popup window down ARG lines.
      If ARG is ‘nil’, then it scrolls near full screen.  This is a
      wrapper around ‘scroll-down-command’ (which see).
 
 
 File: transient.info,  Node: Other Options,  Prev: Other Commands,  Up: Usage
 
 2.9 Other Options
 =================
 
  -- User Option: transient-show-popup
 
      This option controls whether the current transient’s infix and
      suffix commands are shown in the popup buffer.
 
         • If ‘t’ (the default) then the popup buffer is shown as soon as
           a transient prefix command is invoked.
 
         • If ‘nil’, then the popup buffer is not shown unless the user
           explicitly requests it, by pressing an incomplete prefix key
           sequence.
 
         • If a number, then the a brief one-line summary is shown
           instead of the popup buffer.  If zero or negative, then not
           even that summary is shown; only the pressed key itself is
           shown.
 
           The popup is shown when the user explicitly requests it by
           pressing an incomplete prefix key sequence.  Unless this is
           zero, then the popup is shown after that many seconds of
           inactivity (using the absolute value).
 
  -- User Option: transient-enable-popup-navigation
 
      This option controls whether navigation commands are enabled in the
      transient popup buffer.
 
      While a transient is active the transient popup buffer is not the
      current buffer, making it necessary to use dedicated commands to
      act on that buffer itself.  This is disabled by default.  If this
      option is non-nil, then the following features are available:
 
         • ‘<up>’ moves the cursor to the previous suffix.  ‘<down>’
           moves the cursor to the next suffix.  ‘RET’ invokes the suffix
           the cursor is on.
 
         • ‘<mouse-1>’ invokes the clicked on suffix.
 
         • ‘C-s’ and ‘C-r’ start isearch in the popup buffer.
 
  -- User Option: transient-display-buffer-action
 
      This option specifies the action used to display the transient
      popup buffer.  The transient popup buffer is displayed in a window
      using ‘(display-buffer BUFFER transient-display-buffer-action)’.
 
      The value of this option has the form ‘(FUNCTION . ALIST)’, where
      FUNCTION is a function or a list of functions.  Each such function
      should accept two arguments: a buffer to display and an alist of
      the same form as ALIST.  See *note (elisp)Choosing Window:: for
      details.
 
      The default is:
 
      (display-buffer-in-side-window (side .  bottom)
      (inhibit-same-window .  t) (window-parameters (no-other-window .
      t)))
 
      This displays the window at the bottom of the selected frame.
      Another useful FUNCTION is ‘display-buffer-below-selected’, which
      is what ‘magit-popup’ used by default.  For more alternatives see
      *note (elisp)Display Action Functions:: and *note (elisp)Buffer
      Display Action Alists::.
 
      Note that the buffer that was current before the transient buffer
      is shown should remain the current buffer.  Many suffix commands
      act on the thing at point, if appropriate, and if the transient
      buffer became the current buffer, then that would change what is at
      point.  To that effect ‘inhibit-same-window’ ensures that the
      selected window is not used to show the transient buffer.
 
      It may be possible to display the window in another frame, but
      whether that works in practice depends on the window-manager.  If
      the window manager selects the new window (Emacs frame), then that
      unfortunately changes which buffer is current.
 
      If you change the value of this option, then you might also want to
      change the value of ‘transient-mode-line-format’.
 
  -- User Option: transient-mode-line-format
 
      This option controls whether the transient popup buffer has a
      mode-line, separator line, or neither.
 
      If ‘nil’, then the buffer has no mode-line.  If the buffer is not
      displayed right above the echo area, then this probably is not a
      good value.
 
      If ‘line’ (the default), then the buffer also has no mode-line, but
      a thin line is drawn instead, using the background color of the
      face ‘transient-separator’.  Termcap frames cannot display thin
      lines and therefore fallback to treating ‘line’ like ‘nil’.
 
      Otherwise this can be any mode-line format.  See *note (elisp)Mode
      Line Format:: for details.
 
  -- User Option: transient-read-with-initial-input
 
      This option controls whether the last history element is used as
      the initial minibuffer input when reading the value of an infix
      argument from the user.  If ‘nil’, then there is no initial input
      and the first element has to be accessed the same way as the older
      elements.
 
  -- User Option: transient-highlight-mismatched-keys
 
      This option controls whether key bindings of infix commands that do
      not match the respective command-line argument should be
      highlighted.  For other infix commands this option has no effect.
 
      When this option is non-nil, then the key binding for an infix
      argument is highlighted when only a long argument (e.g.
      ‘--verbose’) is specified but no shorthand (e.g ‘-v’).  In the rare
      case that a shorthand is specified but the key binding does not
      match, then it is highlighted differently.
 
      Highlighting mismatched key bindings is useful when learning the
      arguments of the underlying command-line tool; you wouldn’t want to
      learn any short-hands that do not actually exist.
 
      The highlighting is done using one of the faces
      ‘transient-mismatched-key’ and ‘transient-nonstandard-key’.
 
  -- User Option: transient-substitute-key-function
 
      This function is used to modify key bindings.  If the value of this
      option is nil (the default), then no substitution is performed.
 
      This function is called with one argument, the prefix object, and
      must return a key binding description, either the existing key
      description it finds in the ‘key’ slot, or the key description that
      replaces the prefix key.  It could be used to make other
      substitutions, but that is discouraged.
 
      For example, ‘=’ is hard to reach using my custom keyboard layout,
      so I substitute ‘(’ for that, which is easy to reach using a layout
      optimized for lisp.
 
           (setq transient-substitute-key-function
                 (lambda (obj)
                   (let ((key (oref obj key)))
                     (if (string-match "\\`\\(=\\)[a-zA-Z]" key)
                         (replace-match "(" t t key 1)
                       key))))
 
  -- User Option: transient-detect-key-conflicts
 
      This option controls whether key binding conflicts should be
      detected at the time the transient is invoked.  If so, then this
      results in an error, which prevents the transient from being used.
      Because of that, conflicts are ignored by default.
 
      Conflicts cannot be determined earlier, i.e.  when the transient is
      being defined and when new suffixes are being added, because at
      that time there can be false-positives.  It is actually valid for
      multiple suffixes to share a common key binding, provided the
      predicates of those suffixes prevent that more than one of them is
      enabled at a time.
 
  -- User Option: transient-force-fixed-pitch
 
      This option controls whether to force the use of a monospaced font
      in popup buffer.  Even if you use a proportional font for the
      ‘default’ face, you might still want to use a monospaced font in
      transient’s popup buffer.  Setting this option to t causes
      ‘default’ to be remapped to ‘fixed-pitch’ in that buffer.
 
 
 File: transient.info,  Node: Modifying Existing Transients,  Next: Defining New Commands,  Prev: Usage,  Up: Top
 
 3 Modifying Existing Transients
 *******************************
 
 To an extent transients can be customized interactively, see *note
 Enabling and Disabling Suffixes::.  This section explains how existing
 transients can be further modified non-interactively.
 
    The following functions share a few arguments:
 
    • PREFIX is a transient prefix command, a symbol.
 
    • SUFFIX is a transient infix or suffix specification in the same
      form as expected by ‘transient-define-prefix’.  Note that an infix
      is a special kind of suffix.  Depending on context "suffixes" means
      "suffixes (including infixes)" or "non-infix suffixes".  Here it
      means the former.  See *note Suffix Specifications::.
 
      SUFFIX may also be a group in the same form as expected by
      ‘transient-define-prefix’.  See *note Group Specifications::.
 
    • LOC is a command, a key vector, a key description (a string as
      returned by ‘key-description’), or a list specifying coordinates
      (the last element may also be a command or key).  For example ‘(1 0
      -1)’ identifies the last suffix (‘-1’) of the first subgroup (‘0’)
      of the second group (‘1’).
 
      If LOC is a list of coordinates, then it can be used to identify a
      group, not just an individual suffix command.
 
      The function ‘transient-get-suffix’ can be useful to determine
      whether a certain coordination list identifies the suffix or group
      that you expect it to identify.  In hairy cases it may be necessary
      to look at the definition of the transient prefix command.
 
    These functions operate on the information stored in the
 ‘transient--layout’ property of the PREFIX symbol.  Suffix entries in
 that tree are not objects but have the form ‘(LEVEL CLASS PLIST)’, where
 plist should set at least ‘:key’, ‘:description’ and ‘:command’.
 
  -- Function: transient-insert-suffix prefix loc suffix
 
      This function inserts suffix or group SUFFIX into PREFIX before
      LOC.
 
  -- Function: transient-append-suffix prefix loc suffix
 
      This function inserts suffix or group SUFFIX into PREFIX after LOC.
 
  -- Function: transient-replace-suffix prefix loc suffix
 
      This function replaces the suffix or group at LOC in PREFIX with
      suffix or group SUFFIX.
 
  -- Function: transient-remove-suffix prefix loc
 
      This function removes the suffix or group at LOC in PREFIX.
 
  -- Function: transient-get-suffix prefix loc
 
      This function returns the suffix or group at LOC in PREFIX.  The
      returned value has the form mentioned above.
 
  -- Function: transient-suffix-put prefix loc prop value
 
      This function edits the suffix or group at LOC in PREFIX, by
      setting the PROP of its plist to VALUE.
 
    Most of these functions do not signal an error if they cannot perform
 the requested modification.  The functions that insert new suffixes show
 a warning if LOC cannot be found in PREFIX, without signaling an error.
 The reason for doing it like this is that establishing a key binding
 (and that is what we essentially are trying to do here) should not
 prevent the rest of the configuration from loading.  Among these
 functions only ‘transient-get-suffix’ and ‘transient-suffix-put’ may
 signal an error.
 
 
 File: transient.info,  Node: Defining New Commands,  Next: Classes and Methods,  Prev: Modifying Existing Transients,  Up: Top
 
 4 Defining New Commands
 ***********************
 
 * Menu:
 
 * Defining Transients::
 * Binding Suffix and Infix Commands::
 * Defining Suffix and Infix Commands::
 * Using Infix Arguments::
 * Transient State::
 
 
 File: transient.info,  Node: Defining Transients,  Next: Binding Suffix and Infix Commands,  Up: Defining New Commands
 
 4.1 Defining Transients
 =======================
 
 A transient consists of a prefix command and at least one suffix
 command, though usually a transient has several infix and suffix
 commands.  The below macro defines the transient prefix command *and*
 binds the transient’s infix and suffix commands.  In other words, it
 defines the complete transient, not just the transient prefix command
 that is used to invoke that transient.
 
  -- Macro: transient-define-prefix name arglist [docstring] [keyword
           value]... group... [body...]
 
      This macro defines NAME as a transient prefix command and binds the
      transient’s infix and suffix commands.
 
      ARGLIST are the arguments that the prefix command takes.  DOCSTRING
      is the documentation string and is optional.
 
      These arguments can optionally be followed by keyword-value pairs.
      Each key has to be a keyword symbol, either ‘:class’ or a keyword
      argument supported by the constructor of that class.  The
      ‘transient-prefix’ class is used if the class is not specified
      explicitly.
 
      GROUPs add key bindings for infix and suffix commands and specify
      how these bindings are presented in the popup buffer.  At least one
      GROUP has to be specified.  See *note Binding Suffix and Infix
      Commands::.
 
      The BODY is optional.  If it is omitted, then ARGLIST is ignored
      and the function definition becomes:
 
           (lambda ()
             (interactive)
             (transient-setup 'NAME))
 
      If BODY is specified, then it must begin with an ‘interactive’ form
      that matches ARGLIST, and it must call ‘transient-setup’.  It may
      however call that function only when some condition is satisfied.
 
      All transients have a (possibly ‘nil’) value, which is exported
      when suffix commands are called, so that they can consume that
      value.  For some transients it might be necessary to have a sort of
      secondary value, called a "scope".  Such a scope would usually be
      set in the command’s ‘interactive’ form and has to be passed to the
      setup function:
 
           (transient-setup 'NAME nil nil :scope SCOPE)
 
      For example, the scope of the ‘magit-branch-configure’ transient is
      the branch whose variables are being configured.
 
 
 File: transient.info,  Node: Binding Suffix and Infix Commands,  Next: Defining Suffix and Infix Commands,  Prev: Defining Transients,  Up: Defining New Commands
 
 4.2 Binding Suffix and Infix Commands
 =====================================
 
 The macro ‘transient-define-prefix’ is used to define a transient.  This
 defines the actual transient prefix command (see *note Defining
 Transients::) and adds the transient’s infix and suffix bindings, as
 described below.
 
    Users and third-party packages can add additional bindings using
 functions such as ‘transient-insert-suffix’ (See *note Modifying
 Existing Transients::).  These functions take a "suffix specification"
 as one of their arguments, which has the same form as the specifications
 used in ‘transient-define-prefix’.
 
 * Menu:
 
 * Group Specifications::
 * Suffix Specifications::
 
 
 File: transient.info,  Node: Group Specifications,  Next: Suffix Specifications,  Up: Binding Suffix and Infix Commands
 
 4.2.1 Group Specifications
 --------------------------
 
 The suffix and infix commands of a transient are organized in groups.
 The grouping controls how the descriptions of the suffixes are outlined
 visually but also makes it possible to set certain properties for a set
 of suffixes.
 
    Several group classes exist, some of which organize suffixes in
 subgroups.  In most cases the class does not have to be specified
 explicitly, but see *note Group Classes::.
 
    Groups are specified in the call to ‘transient-define-prefix’, using
 vectors.  Because groups are represented using vectors, we cannot use
 square brackets to indicate an optional element and instead use curly
 brackets to do the latter.
 
    Group specifications then have this form:
 
      [{LEVEL} {DESCRIPTION} {KEYWORD VALUE}... ELEMENT...]
 
    The LEVEL is optional and defaults to 4.  See *note Enabling and
 Disabling Suffixes::.
 
    The DESCRIPTION is optional.  If present it is used as the heading of
 the group.
 
    The KEYWORD-VALUE pairs are optional.  Each keyword has to be a
 keyword symbol, either ‘:class’ or a keyword argument supported by the
 constructor of that class.
 
    • One of these keywords, ‘:description’, is equivalent to specifying
      DESCRIPTION at the very beginning of the vector.  The
      recommendation is to use ‘:description’ if some other keyword is
      also used, for consistency, or DESCRIPTION otherwise, because it
      looks better.
 
    • Likewise ‘:level’ is equivalent to LEVEL.
 
    • Other important keywords include the ‘:if...’ keywords.  These
      keywords control whether the group is available in a certain
      situation.
 
      For example, one group of the ‘magit-rebase’ transient uses ‘:if
      magit-rebase-in-progress-p’, which contains the suffixes that are
      useful while rebase is already in progress; and another that uses
      ‘:if-not magit-rebase-in-progress-p’, which contains the suffixes
      that initiate a rebase.
 
      These predicates can also be used on individual suffixes and are
      only documented once, see *note Predicate Slots::.
 
    • The value of ‘:hide’, if non-nil, is a predicate that controls
      whether the group is hidden by default.  The key bindings for
      suffixes of a hidden group should all use the same prefix key.
      Pressing that prefix key should temporarily show the group and its
      suffixes, which assumes that a predicate like this is used:
 
           (lambda ()
             (eq (car transient--redisplay-key)
                 ?\C-c)) ; the prefix key shared by all bindings
 
    • The value of ‘:setup-children’, if non-nil, is a function that
      takes two arguments the group object itself and a list of children.
      The children are given as a, potentially empty, list consisting of
      either group or suffix specifications.  It can make arbitrary
      changes to the children including constructing new children from
      scratch.  Also see ‘transient-setup-children’.
 
    • The boolean ‘:pad-keys’ argument controls whether keys of all
      suffixes contained in a group are right padded, effectively
      aligning the descriptions.
 
    The ELEMENTs are either all subgroups (vectors), or all suffixes
 (lists) and strings.  (At least currently no group type exists that
 would allow mixing subgroups with commands at the same level, though in
 principle there is nothing that prevents that.)
 
    If the ELEMENTs are not subgroups, then they can be a mixture of
 lists that specify commands and strings.  Strings are inserted verbatim.
 The empty string can be used to insert gaps between suffixes, which is
 particularly useful if the suffixes are outlined as a table.
 
    Variables are supported inside group specifications.  For example in
 place of a direct subgroup specification, a variable can be used whose
 value is a vector that qualifies as a group specification.  Likewise a
 variable can be used where a suffix specification is expected.  Lists of
 group or suffix specifications are also supported.  Indirect
 specifications are resolved when the transient prefix is being defined.
 
    The form of suffix specifications is documented in the next node.
 
 
 File: transient.info,  Node: Suffix Specifications,  Prev: Group Specifications,  Up: Binding Suffix and Infix Commands
 
 4.2.2 Suffix Specifications
 ---------------------------
 
 A transient’s suffix and infix commands are bound when the transient
 prefix command is defined using ‘transient-define-prefix’, see *note
 Defining Transients::.  The commands are organized into groups, see
 *note Group Specifications::.  Here we describe the form used to bind an
 individual suffix command.
 
    The same form is also used when later binding additional commands
 using functions such as ‘transient-insert-suffix’, see *note Modifying
 Existing Transients::.
 
    Note that an infix is a special kind of suffix.  Depending on context
 "suffixes" means "suffixes (including infixes)" or "non-infix suffixes".
 Here it means the former.
 
    Suffix specifications have this form:
 
      ([LEVEL] [KEY] [DESCRIPTION] COMMAND|ARGUMENT [KEYWORD VALUE]...)
 
    LEVEL, KEY and DESCRIPTION can also be specified using the KEYWORDs
 ‘:level’, ‘:key’ and ‘:description’.  If the object that is associated
 with COMMAND sets these properties, then they do not have to be
 specified here.  You can however specify them here anyway, possibly
 overriding the object’s values just for the binding inside this
 transient.
 
    • LEVEL is the suffix level, an integer between 1 and 7.  See *note
      Enabling and Disabling Suffixes::.
 
    • KEY is the key binding, either a vector or key description string.
 
    • DESCRIPTION is the description, either a string or a function that
      returns a string.  The function should be a lambda expression to
      avoid ambiguity.  In some cases a symbol that is bound as a
      function would also work but to be safe you should use
      ‘:description’ in that case.
 
    The next element is either a command or an argument.  This is the
 only argument that is mandatory in all cases.
 
    • Usually COMMAND is a symbol that is bound as a function, which has
      to be defined or at least autoloaded as a command by the time the
      containing prefix command is invoked.
 
      Any command will do; it does not need to have an object associated
      with it (as would be the case if ‘transient-define-suffix’ or
      ‘transient-define-infix’ were used to define it).
 
      The command can also be a closure or lambda expression, but that
      should only be used for dynamic transients whose suffixes are
      defined when the prefix command is invoked.  See information about
      the ‘:setup-children’ function in *note Group Specifications::.
 
      As mentioned above, the object that is associated with a command
      can be used to set the default for certain values that otherwise
      have to be set in the suffix specification.  Therefore if there is
      no object, then you have to make sure to specify the KEY and the
      DESCRIPTION.
 
      As a special case, if you want to add a command that might be
      neither defined nor autoloaded, you can use a workaround like:
 
           (transient-insert-suffix 'some-prefix "k"
             '("!" "Ceci n'est pas une commande" no-command
               :if (lambda () (featurep 'no-library))))
 
      Instead of ‘featurep’ you could also use ‘require’ with a non-nil
      value for NOERROR.
 
    • The mandatory argument can also be a command-line argument, a
      string.  In that case an anonymous command is defined and bound.
 
      Instead of a string, this can also be a list of two strings, in
      which case the first string is used as the short argument (which
      can also be specified using ‘:shortarg’) and the second as the long
      argument (which can also be specified using ‘:argument’).
 
      Only the long argument is displayed in the popup buffer.  See
      ‘transient-detect-key-conflicts’ for how the short argument may be
      used.
 
      Unless the class is specified explicitly, the appropriate class is
      guessed based on the long argument.  If the argument ends with "=​"
      (e.g.  "–format=") then ‘transient-option’ is used, otherwise
      ‘transient-switch’.
 
    Finally, details can be specified using optional KEYWORD-VALUE pairs.
 Each keyword has to be a keyword symbol, either ‘:class’ or a keyword
 argument supported by the constructor of that class.  See *note Suffix
 Slots::.
 
 
 File: transient.info,  Node: Defining Suffix and Infix Commands,  Next: Using Infix Arguments,  Prev: Binding Suffix and Infix Commands,  Up: Defining New Commands
 
 4.3 Defining Suffix and Infix Commands
 ======================================
 
 Note that an infix is a special kind of suffix.  Depending on context
 "suffixes" means "suffixes (including infixes)" or "non-infix suffixes".
 
  -- Macro: transient-define-suffix name arglist [docstring] [keyword
           value]... body...
 
      This macro defines NAME as a transient suffix command.
 
      ARGLIST are the arguments that the command takes.  DOCSTRING is the
      documentation string and is optional.
 
      These arguments can optionally be followed by keyword-value pairs.
      Each keyword has to be a keyword symbol, either ‘:class’ or a
      keyword argument supported by the constructor of that class.  The
      ‘transient-suffix’ class is used if the class is not specified
      explicitly.
 
      The BODY must begin with an ‘interactive’ form that matches
      ARGLIST.  The infix arguments are usually accessed by using
      ‘transient-args’ inside ‘interactive’.
 
  -- Macro: transient-define-infix name arglist [docstring] [keyword
           value]...
 
      This macro defines NAME as a transient infix command.
 
      ARGLIST is always ignored (but mandatory never-the-less) and
      reserved for future use.  DOCSTRING is the documentation string and
      is optional.
 
      The keyword-value pairs are mandatory.  All transient infix
      commands are ‘equal’ to each other (but not ‘eq’), so it is
      meaningless to define an infix command without also setting at
      least ‘:class’ and one other keyword (which it is depends on the
      used class, usually ‘:argument’ or ‘:variable’).
 
      Each keyword has to be a keyword symbol, either ‘:class’ or a
      keyword argument supported by the constructor of that class.  The
      ‘transient-switch’ class is used if the class is not specified
      explicitly.
 
      The function definition is always:
 
           (lambda ()
             (interactive)
             (let ((obj (transient-suffix-object)))
               (transient-infix-set obj (transient-infix-read obj)))
             (transient--show))
 
      ‘transient-infix-read’ and ‘transient-infix-set’ are generic
      functions.  Different infix commands behave differently because the
      concrete methods are different for different infix command classes.
      In rare cases the above command function might not be suitable,
      even if you define your own infix command class.  In that case you
      have to use ‘transient-suffix-command’ to define the infix command
      and use ‘t’ as the value of the ‘:transient’ keyword.
 
  -- Macro: transient-define-argument name arglist [docstring] [keyword
           value]...
 
      This macro defines NAME as a transient infix command.
 
      This is an alias for ‘transient-define-infix’.  Only use this alias
      to define an infix command that actually sets an infix argument.
      To define an infix command that, for example, sets a variable, use
      ‘transient-define-infix’ instead.
 
 
 File: transient.info,  Node: Using Infix Arguments,  Next: Transient State,  Prev: Defining Suffix and Infix Commands,  Up: Defining New Commands
 
 4.4 Using Infix Arguments
 =========================
 
 The function and the variables described below allow suffix commands to
 access the value of the transient from which they were invoked; which is
 the value of its infix arguments.  These variables are set when the user
 invokes a suffix command that exits the transient, but before actually
 calling the command.
 
    When returning to the command-loop after calling the suffix command,
 the arguments are reset to ‘nil’ (which causes the function to return
 ‘nil’ too).
 
    Like for Emacs’ prefix arguments it is advisable, but not mandatory,
 to access the infix arguments inside the command’s ‘interactive’ form.
 The preferred way of doing that is to call the ‘transient-args’
 function, which for infix arguments serves about the same purpose as
 ‘prefix-arg’ serves for prefix arguments.
 
  -- Function: transient-args prefix
 
      This function returns the value of the transient prefix command
      PREFIX.
 
      If the current command was invoked from the transient prefix
      command PREFIX, then it returns the active infix arguments.  If the
      current command was not invoked from PREFIX, then it returns the
      set, saved or default value for PREFIX.
 
  -- Function: transient-arg-value arg args
 
      This function return the value of ARG as it appears in ARGS.
 
      For a switch a boolean is returned.  For an option the value is
      returned as a string, using the empty string for the empty value,
      or nil if the option does not appear in ARGS.
 
  -- Function: transient-suffixes prefix
 
      This function returns the suffixes of the transient prefix command
      PREFIX.  This is a list of objects.  This function should only be
      used if you need the objects (as opposed to just their values) and
      if the current command is not being invoked from PREFIX.
 
  -- Variable: transient-current-suffixes
 
      The suffixes of the transient from which this suffix command was
      invoked.  This is a list of objects.  Usually it is sufficient to
      instead use the function ‘transient-args’, which returns a list of
      values.  In complex cases it might be necessary to use this
      variable instead, i.e.  if you need access to information beside
      the value.
 
  -- Variable: transient-current-prefix
 
      The transient from which this suffix command was invoked.  The
      returned value is a ‘transient-prefix’ object, which holds
      information associated with the transient prefix command.
 
  -- Variable: transient-current-command
 
      The transient from which this suffix command was invoked.  The
      returned value is a symbol, the transient prefix command.
 
 
 File: transient.info,  Node: Transient State,  Prev: Using Infix Arguments,  Up: Defining New Commands
 
 4.5 Transient State
 ===================
 
 Invoking a transient prefix command "activates" the respective
 transient, i.e.  it puts a transient keymap into effect, which binds the
 transient’s infix and suffix commands.
 
    The default behavior while a transient is active is as follows:
 
    • Invoking an infix command does not affect the transient state; the
      transient remains active.
 
    • Invoking a (non-infix) suffix command "deactivates" the transient
      state by removing the transient keymap and performing some
      additional cleanup.
 
    • Invoking a command that is bound in a keymap other than the
      transient keymap is disallowed and trying to do so results in a
      warning.  This does not "deactivate" the transient.
 
    But these are just the defaults.  Whether a certain command
 deactivates or "exits" the transient is configurable.  There is more
 than one way in which a command can be "transient" or "non-transient";
 the exact behavior is implemented by calling a so-called "pre-command"
 function.  Whether non-suffix commands are allowed to be called is
 configurable per transient.
 
    • The transient-ness of suffix commands (including infix commands) is
      controlled by the value of their ‘transient’ slot, which can be set
      either when defining the command or when adding a binding to a
      transient while defining the respective transient prefix command.
 
      Valid values are booleans and the pre-commands described below.
 
         • ‘t’ is equivalent to ‘transient--do-stay’.
 
         • ‘nil’ is equivalent to ‘transient--do-exit’.
 
         • If ‘transient’ is unbound (and that is actually the default
           for non-infix suffixes) then the value of the prefix’s
           ‘transient-suffix’ slot is used instead.  The default value of
           that slot is ‘nil’, so the suffix’s ‘transient’ slot being
           unbound is essentially equivalent to it being ‘nil’.
 
    • A suffix command can be a prefix command itself, i.e.  a
      "sub-prefix".  While a sub-prefix is active we nearly always want
      ‘C-g’ to take the user back to the "super-prefix".  However in rare
      cases this may not be desirable, and that makes the following
      complication necessary:
 
      For ‘transient-suffix’ objects the ‘transient’ slot is unbound.  We
      can ignore that for the most part because, as stated above, ‘nil’
      and the slot being unbound are equivalent, and mean "do exit".
      That isn’t actually true for suffixes that are sub-prefixes though.
      For such suffixes unbound means "do exit but allow going back",
      which is the default, while ‘nil’ means "do exit permanently",
      which requires that slot to be explicitly set to that value.
 
    • The transient-ness of certain built-in suffix commands is specified
      using ‘transient-predicate-map’.  This is a special keymap, which
      binds commands to pre-commands (as opposed to keys to commands) and
      takes precedence over the ‘transient’ slot.
 
    The available pre-command functions are documented below.  They are
 called by ‘transient--pre-command’, a function on ‘pre-command-hook’ and
 the value that they return determines whether the transient is exited.
 To do so the value of one of the constants ‘transient--exit’ or
 ‘transient--stay’ is used (that way we don’t have to remember if ‘t’
 means "exit" or "stay").
 
    Additionally these functions may change the value of ‘this-command’
 (which explains why they have to be called using ‘pre-command-hook’),
 call ‘transient-export’, ‘transient--stack-zap’ or
 ‘transient--stack-push’; and set the values of ‘transient--exitp’,
 ‘transient--helpp’ or ‘transient--editp’.
 
 Pre-commands for Infixes
 ------------------------
 
 The default for infixes is ‘transient--do-stay’.  This is also the only
 function that makes sense for infixes.
 
  -- Function: transient--do-stay
 
      Call the command without exporting variables and stay transient.
 
 Pre-commands for Suffixes
 -------------------------
 
 The default for suffixes is ‘transient--do-exit’.
 
  -- Function: transient--do-exit
 
      Call the command after exporting variables and exit the transient.
 
  -- Function: transient--do-call
 
      Call the command after exporting variables and stay transient.
 
  -- Function: transient--do-replace
 
      Call the transient prefix command, replacing the active transient.
 
      This is used for suffixes that are prefixes themselves, i.e.  for
      sub-prefixes.
 
 Pre-commands for Non-Suffixes
 -----------------------------
 
 The default for non-suffixes, i.e commands that are bound in other
 keymaps beside the transient keymap, is ‘transient--do-warn’.  Silently
 ignoring the user-error is also an option, though probably not a good
 one.
 
    If you want to let the user invoke non-suffix commands, then use
 ‘transient--do-stay’ as the value of the prefix’s ‘transient-non-suffix’
 slot.
 
  -- Function: transient--do-warn
 
      Call ‘transient-undefined’ and stay transient.
 
  -- Function: transient--do-noop
 
      Call ‘transient-noop’ and stay transient.
 
 Special Pre-Commands
 --------------------
 
  -- Function: transient--do-quit-one
 
      If active, quit help or edit mode, else exit the active transient.
 
      This is used when the user pressed ‘C-g’.
 
  -- Function: transient--do-quit-all
 
      Exit all transients without saving the transient stack.
 
      This is used when the user pressed ‘C-q’.
 
  -- Function: transient--do-suspend
 
      Suspend the active transient, saving the transient stack.
 
      This is used when the user pressed ‘C-z’.
 
 
 File: transient.info,  Node: Classes and Methods,  Next: Related Abstractions and Packages,  Prev: Defining New Commands,  Up: Top
 
 5 Classes and Methods
 *********************
 
 Transient uses classes and generic functions to make it possible to
 define new types of suffix commands that are similar to existing types,
 but behave differently in some aspects.  It does the same for groups and
 prefix commands, though at least for prefix commands that *currently*
 appears to be less important.
 
    Every prefix, infix and suffix command is associated with an object,
 which holds information that controls certain aspects of its behavior.
 This happens in two ways.
 
    • Associating a command with a certain class gives the command a
      type.  This makes it possible to use generic functions to do
      certain things that have to be done differently depending on what
      type of command it acts on.
 
      That in turn makes it possible for third-parties to add new types
      without having to convince the maintainer of Transient that that
      new type is important enough to justify adding a special case to a
      dozen or so functions.
 
    • Associating a command with an object makes it possible to easily
      store information that is specific to that particular command.
 
      Two commands may have the same type, but obviously their key
      bindings and descriptions still have to be different, for example.
 
      The values of some slots are functions.  The ‘reader’ slot for
      example holds a function that is used to read a new value for an
      infix command.  The values of such slots are regular functions.
 
      Generic functions are used when a function should do something
      different based on the type of the command, i.e.  when all commands
      of a certain type should behave the same way but different from the
      behavior for other types.  Object slots that hold a regular
      function as value are used when the task that they perform is
      likely to differ even between different commands of the same type.
 
 * Menu:
 
 * Group Classes::
 * Group Methods::
 * Prefix Classes::
 * Suffix Classes::
 * Suffix Methods::
 * Prefix Slots::
 * Suffix Slots::
 * Predicate Slots::
 
 
 File: transient.info,  Node: Group Classes,  Next: Group Methods,  Up: Classes and Methods
 
 5.1 Group Classes
 =================
 
 The type of a group can be specified using the ‘:class’ property at the
 beginning of the class specification, e.g.  ‘[:class transient-columns
 ...]’ in a call to ‘transient-define-prefix’.
 
    • The abstract ‘transient-child’ class is the base class of both
      ‘transient-group’ (and therefore all groups) as well as of
      ‘transient-suffix’ (and therefore all suffix and infix commands).
 
      This class exists because the elements (aka "children") of certain
      groups can be other groups instead of suffix and infix commands.
 
    • The abstract ‘transient-group’ class is the superclass of all other
      group classes.
 
    • The ‘transient-column’ class is the simplest group.
 
      This is the default "flat" group.  If the class is not specified
      explicitly and the first element is not a vector (i.e.  not a
      group), then this class is used.
 
      This class displays each element on a separate line.
 
    • The ‘transient-row’ class displays all elements on a single line.
 
    • The ‘transient-columns’ class displays commands organized in
      columns.
 
      Direct elements have to be groups whose elements have to be
      commands or strings.  Each subgroup represents a column.  This
      class takes care of inserting the subgroups’ elements.
 
      This is the default "nested" group.  If the class is not specified
      explicitly and the first element is a vector (i.e.  a group), then
      this class is used.
 
    • The ‘transient-subgroups’ class wraps other groups.
 
      Direct elements have to be groups whose elements have to be
      commands or strings.  This group inserts an empty line between
      subgroups.  The subgroups themselves are responsible for displaying
      their elements.
 
 
 File: transient.info,  Node: Group Methods,  Next: Prefix Classes,  Prev: Group Classes,  Up: Classes and Methods
 
 5.2 Group Methods
 =================
 
  -- Function: transient-setup-children group children
 
      This generic function can be used to setup the children or a group.
 
      The default implementation usually just returns the children
      unchanged, but if the ‘setup-children’ slot of GROUP is non-nil,
      then it calls that function with CHILDREN as the only argument and
      returns the value.
 
      The children are given as a, potentially empty, list consisting of
      either group or suffix specifications.  These functions can make
      arbitrary changes to the children including constructing new
      children from scratch.
 
  -- Function: transient--insert-group group
 
      This generic function formats the group and its elements and
      inserts the result into the current buffer, which is a temporary
      buffer.  The contents of that buffer are later inserted into the
      popup buffer.
 
      Functions that are called by this function may need to operate in
      the buffer from which the transient was called.  To do so they can
      temporarily make the ‘transient--source-buffer’ the current buffer.
 
 
 File: transient.info,  Node: Prefix Classes,  Next: Suffix Classes,  Prev: Group Methods,  Up: Classes and Methods
 
 5.3 Prefix Classes
 ==================
 
 Currently the ‘transient-prefix’ class is being used for all prefix
 commands and there is only a single generic function that can be
 specialized based on the class of a prefix command.
 
  -- Function: transient--history-init obj
 
      This generic function is called while setting up the transient and
      is responsible for initializing the ‘history’ slot.  This is the
      transient-wide history; many individual infixes also have a history
      of their own.
 
      The default (and currently only) method extracts the value from the
      global variable ‘transient-history’.
 
    A transient prefix command’s object is stored in the
 ‘transient--prefix’ property of the command symbol.  While a transient
 is active, a clone of that object is stored in the variable
 ‘transient--prefix’.  A clone is used because some changes that are made
 to the active transient’s object should not affect later invocations.
 
 
 File: transient.info,  Node: Suffix Classes,  Next: Suffix Methods,  Prev: Prefix Classes,  Up: Classes and Methods
 
 5.4 Suffix Classes
 ==================
 
    • All suffix and infix classes derive from ‘transient-suffix’, which
      in turn derives from ‘transient-child’, from which
      ‘transient-group’ also derives (see *note Group Classes::).
 
    • All infix classes derive from the abstract ‘transient-infix’ class,
      which in turn derives from the ‘transient-suffix’ class.
 
      Infixes are a special type of suffixes.  The primary difference is
      that infixes always use the ‘transient--do-stay’ pre-command, while
      non-infix suffixes use a variety of pre-commands (see *note
      Transient State::).  Doing that is most easily achieved by using
      this class, though theoretically it would be possible to define an
      infix class that does not do so.  If you do that then you get to
      implement many methods.
 
      Also, infixes and non-infix suffixes are usually defined using
      different macros (see *note Defining Suffix and Infix Commands::).
 
    • Classes used for infix commands that represent arguments should be
      derived from the abstract ‘transient-argument’ class.
 
    • The ‘transient-switch’ class (or a derived class) is used for infix
      arguments that represent command-line switches (arguments that do
      not take a value).
 
    • The ‘transient-option’ class (or a derived class) is used for infix
      arguments that represent command-line options (arguments that do
      take a value).
 
    • The ‘transient-switches’ class can be used for a set of mutually
      exclusive command-line switches.
 
    • The ‘transient-files’ class can be used for a "–" argument that
      indicates that all remaining arguments are files.
 
    • Classes used for infix commands that represent variables should
      derived from the abstract ‘transient-variables’ class.
 
    Magit defines additional classes, which can serve as examples for the
 fancy things you can do without modifying Transient.  Some of these
 classes will likely get generalized and added to Transient.  For now
 they are very much subject to change and not documented.
 
 
 File: transient.info,  Node: Suffix Methods,  Next: Prefix Slots,  Prev: Suffix Classes,  Up: Classes and Methods
 
 5.5 Suffix Methods
 ==================
 
 To get information about the methods implementing these generic
 functions use ‘describe-function’.
 
 * Menu:
 
 * Suffix Value Methods::
 * Suffix Format Methods::
 
 
 File: transient.info,  Node: Suffix Value Methods,  Next: Suffix Format Methods,  Up: Suffix Methods
 
 5.5.1 Suffix Value Methods
 --------------------------
 
  -- Function: transient-init-value obj
 
      This generic function sets the initial value of the object OBJ.
 
      This function is called for all suffix commands, but unless a
      concrete method is implemented this falls through to the default
      implementation, which is a noop.  In other words this usually only
      does something for infix commands, but note that this is not
      implemented for the abstract class ‘transient-infix’, so if your
      class derives from that directly, then you must implement a method.
 
  -- Function: transient-infix-read obj
 
      This generic function determines the new value of the infix object
      OBJ.
 
      This function merely determines the value; ‘transient-infix-set’ is
      used to actually store the new value in the object.
 
      For most infix classes this is done by reading a value from the
      user using the reader specified by the ‘reader’ slot (using the
      ‘transient-infix-value’ method described below).
 
      For some infix classes the value is changed without reading
      anything in the minibuffer, i.e.  the mere act of invoking the
      infix command determines what the new value should be, based on the
      previous value.
 
  -- Function: transient-prompt obj
 
      This generic function returns the prompt to be used to read infix
      object OBJ’s value.
 
  -- Function: transient-infix-set obj value
 
      This generic function sets the value of infix object OBJ to VALUE.
 
  -- Function: transient-infix-value obj
 
      This generic function returns the value of the suffix object OBJ.
 
      This function is called by ‘transient-args’ (which see), meaning
      this function is how the value of a transient is determined so that
      the invoked suffix command can use it.
 
      Currently most values are strings, but that is not set in stone.
      ‘nil’ is not a value, it means "no value".
 
      Usually only infixes have a value, but see the method for
      ‘transient-suffix’.
 
  -- Function: transient-init-scope obj
 
      This generic function sets the scope of the suffix object OBJ.
 
      The scope is actually a property of the transient prefix, not of
      individual suffixes.  However it is possible to invoke a suffix
      command directly instead of from a transient.  In that case, if the
      suffix expects a scope, then it has to determine that itself and
      store it in its ‘scope’ slot.
 
      This function is called for all suffix commands, but unless a
      concrete method is implemented this falls through to the default
      implementation, which is a noop.
 
 
 File: transient.info,  Node: Suffix Format Methods,  Prev: Suffix Value Methods,  Up: Suffix Methods
 
 5.5.2 Suffix Format Methods
 ---------------------------
 
  -- Function: transient-format obj
 
      This generic function formats and returns OBJ for display.
 
      When this function is called, then the current buffer is some
      temporary buffer.  If you need the buffer from which the prefix
      command was invoked to be current, then do so by temporarily making
      ‘transient--source-buffer’ current.
 
  -- Function: transient-format-key obj
 
      This generic function formats OBJ’s ‘key’ for display and returns
      the result.
 
  -- Function: transient-format-description obj
 
      This generic function formats OBJ’s ‘description’ for display and
      returns the result.
 
  -- Function: transient-format-value obj
 
      This generic function formats OBJ’s value for display and returns
      the result.
 
  -- Function: transient-show-help obj
 
      Show help for the prefix, infix or suffix command represented by
      OBJ.
 
      For prefixes, show the info manual, if that is specified using the
      ‘info-manual’ slot.  Otherwise show the manpage if that is
      specified using the ‘man-page’ slot.  Otherwise show the command’s
      doc string.
 
      For suffixes, show the command’s doc string.
 
      For infixes, show the manpage if that is specified.  Otherwise show
      the command’s doc string.
 
 
 File: transient.info,  Node: Prefix Slots,  Next: Suffix Slots,  Prev: Suffix Methods,  Up: Classes and Methods
 
 5.6 Prefix Slots
 ================
 
    • ‘man-page’ or ‘info-manual’ can be used to specify the
      documentation for the prefix and its suffixes.  The command
      ‘transient-help’ uses the method ‘transient-show-help’ (which see)
      to lookup and use these values.
 
    • ‘history-key’ If multiple prefix commands should share a single
      value, then this slot has to be set to the same value for all of
      them.  You probably don’t want that.
 
    • ‘transient-suffix’ and ‘transient-non-suffix’ play a part when
      determining whether the currently active transient prefix command
      remains active/transient when a suffix or abitrary non-suffix
      command is invoked.  See *note Transient State::.
 
    • ‘incompatible’ A list of lists.  Each sub-list specifies a set of
      mutually exclusive arguments.  Enabling one of these arguments
      causes the others to be disabled.  An argument may appear in
      multiple sub-lists.
 
    • ‘scope’ For some transients it might be necessary to have a sort of
      secondary value, called a "scope".  See ‘transient-define-prefix’.
 
 Internal Prefix Slots
 ---------------------
 
 These slots are mostly intended for internal use.  They should not be
 set in calls to ‘transient-define-prefix’.
 
    • ‘prototype’ When a transient prefix command is invoked, then a
      clone of that object is stored in the global variable
      ‘transient--prefix’ and the prototype is stored in the clone’s
      ‘prototype’ slot.
 
    • ‘command’ The command, a symbol.  Each transient prefix command
      consists of a command, which is stored in a symbol’s function slot
      and an object, which is stored in the ‘transient--prefix’ property
      of the same symbol.
 
    • ‘level’ The level of the prefix commands.  The suffix commands
      whose layer is equal or lower are displayed.  See *note Enabling
      and Disabling Suffixes::.
 
    • ‘value’ The likely outdated value of the prefix.  Instead of
      accessing this slot directly you should use the function
      ‘transient-get-value’, which is guaranteed to return the up-to-date
      value.
 
    • ‘history’ and ‘history-pos’ are used to keep track of historic
      values.  Unless you implement your own ‘transient-infix-read’
      method you should not have to deal with these slots.
 
 
 File: transient.info,  Node: Suffix Slots,  Next: Predicate Slots,  Prev: Prefix Slots,  Up: Classes and Methods
 
 5.7 Suffix Slots
 ================
 
 Here we document most of the slots that are only available for suffix
 objects.  Some slots are shared by suffix and group objects, they are
 documented in *note Predicate Slots::.
 
    Also see *note Suffix Classes::.
 
 Slots of ‘transient-suffix’
 ---------------------------
 
    • ‘key’ The key, a key vector or a key description string.
 
    • ‘command’ The command, a symbol.
 
    • ‘transient’ Whether to stay transient.  See *note Transient
      State::.
 
    • ‘format’ The format used to display the suffix in the popup buffer.
      It must contain the following %-placeholders:
 
         • ‘%k’ For the key.
 
         • ‘%d’ For the description.
 
         • ‘%v’ For the infix value.  Non-infix suffixes don’t have a
           value.
 
    • ‘description’ The description, either a string or a function that
      is called with no argument and returns a string.
 
 Slots of ‘transient-infix’
 --------------------------
 
 Some of these slots are only meaningful for some of the subclasses.
 They are defined here anyway to allow sharing certain methods.
 
    • ‘argument’ The long argument, e.g.  ‘--verbose’.
 
    • ‘shortarg’ The short argument, e.g.  ‘-v’.
 
    • ‘value’ The value.  Should not be accessed directly.
 
    • ‘init-value’ Function that is responsable for setting the object’s
      value.  If bound, then this is called with the object as the only
      argument.  Usually this is not bound, in which case the object’s
      primary ‘transient-init-value’ method is called instead.
 
    • ‘unsavable’ Whether the value of the suffix is not saved as part of
      the prefixes.
 
    • ‘multi-value’ For options, whether the option can have multiple
      values.  If non-nil, then default to use
      ‘completing-read-multiple’.
 
    • ‘always-read’ For options, whether to read a value on every
      invocation.  If this is nil, then options that have a value are
      simply unset and have to be invoked a second time to set a new
      value.
 
    • ‘allow-empty’ For options, whether the empty string is a valid
      value.
 
    • ‘history-key’ The key used to store the history.  This defaults to
      the command name.  This is useful when multiple infixes should
      share the same history because their values are of the same kind.
 
    • ‘reader’ The function used to read the value of an infix.  Not used
      for switches.  The function takes three arguments, PROMPT,
      INITIAL-INPUT and HISTORY, and must return a string.
 
    • ‘prompt’ The prompt used when reading the value, either a string or
      a function that takes the object as the only argument and which
      returns a prompt string.
 
    • ‘choices’ A list of valid values.  How exactly that is used depends
      on the class of the object.
 
 Slots of ‘transient-variable’
 -----------------------------
 
    • ‘variable’ The variable.
 
 Slots of ‘transient-switches’
 -----------------------------
 
    • ‘argument-format’ The display format.  Must contain ‘%s’, one of
      the ‘choices’ is substituted for that.  E.g.  ‘--%s-order’.
 
    • ‘argument-regexp’ The regexp used to match any one of the switches.
      E.g.  ‘\\(--\\(topo\\|author-date\\|date\\)-order\\)’.
 
 
 File: transient.info,  Node: Predicate Slots,  Prev: Suffix Slots,  Up: Classes and Methods
 
 5.8 Predicate Slots
 ===================
 
 Suffix and group objects share some predicate slots that control whether
 a group or suffix should be available depending on some state.  Only one
 of these slots can be used at the same time.  It is undefined what
 happens if you use more than one.
 
    • ‘if’ Enable if predicate returns non-nil.
 
    • ‘if-not’ Enable if predicate returns nil.
 
    • ‘if-non-nil’ Enable if variable’s value is non-nil.
 
    • ‘if-nil’ Enable if variable’s value is nil.
 
    • ‘if-mode’ Enable if major-mode matches value.
 
    • ‘if-not-mode’ Enable if major-mode does not match value.
 
    • ‘if-derived’ Enable if major-mode derives from value.
 
    • ‘if-not-derived’ Enable if major-mode does not derive from value.
 
    One more slot is shared between group and suffix classes, ‘level’.
 Like the slots documented above, it is a predicate, but it is used for a
 different purpose.  The value has to be an integer between 1 and 7.
 ‘level’ controls whether a suffix or a group should be available
 depending on user preference.  See *note Enabling and Disabling
 Suffixes::.
 
 
 File: transient.info,  Node: Related Abstractions and Packages,  Next: FAQ,  Prev: Classes and Methods,  Up: Top
 
 6 Related Abstractions and Packages
 ***********************************
 
 * Menu:
 
 * Comparison With Prefix Keys and Prefix Arguments::
 * Comparison With Other Packages::
 
 
 File: transient.info,  Node: Comparison With Prefix Keys and Prefix Arguments,  Next: Comparison With Other Packages,  Up: Related Abstractions and Packages
 
 6.1 Comparison With Prefix Keys and Prefix Arguments
 ====================================================
 
 While transient commands were inspired by regular prefix keys and prefix
 arguments, they are also quite different and much more complex.
 
    The following diagrams illustrate some of the differences.
 
    • ‘(c)’ represents a return to the command loop.
 
    • ‘(+)’ represents the user’s choice to press one key or another.
 
    • ‘{WORD}’ are possible behaviors.
 
    • ‘{NUMBER}’ is a footnote.
 
 Regular Prefix Commands
 -----------------------
 
 See *note (elisp)Prefix Keys::.
 
                                        ,--> command1 --> (c)
                                        |
      (c)-(+)-> prefix command or key --+--> command2 --> (c)
                                        |
                                        `--> command3 --> (c)
 
 Regular Prefix Arguments
 ------------------------
 
 See *note (elisp)Prefix Command Arguments::.
 
              ,----------------------------------,
              |                                  |
              v                                  |
      (c)-(+)---> prefix argument command --(c)-(+)-> any command --> (c)
                     |                                        ^        |
                     |                                        |        |
                     `-- sets or changes --, ,-- maybe used --'        |
                                           | |                         |
                                           v |                         |
                                prefix argument state                  |
                                            ^                          |
                                            |                          |
                                            `-------- discards --------'
 
 Transients
 ----------
 
 (∩｀-´)⊃━☆ﾟ.*･｡ﾟ
 
    This diagram ignores the infix value and external state:
 
      (c)
       |        ,- {stay} ------<-,-<------------<-,-<---,
      (+)       |                 |                |     |
       |        |                 |                |     |
       |        |   ,--> infix1 --|                |     |
       |        |   |             |                |     |
       |        |   |--> infix2 --|                |     |
       v        v   |             |                |     |
       prefix -(c)-(+)-> infix3 --'                ^     |
                    |                              |     |
                    |---------------> suffix1 -->--|     |
                    |                              |     |
                    |---------------> suffix2 ----{1}------> {exit} --> (c)
                    |                                    |
                    |---------------> suffix3 -------------> {exit} --> (c)
                    |                                    |
                    `--> any command --{2}-> {warn} -->--|
                                        |                |
                                        |--> {noop} -->--|
                                        |                |
                                        |--> {call} -->--'
                                        |
                                        `------------------> {exit} --> (c)
 
    This diagram takes the infix value into account to an extend, while
 still ignoring external state:
 
      (c)
       |        ,- {stay} ------<-,-<------------<-,-<---,
      (+)       |                 |                |     |
       |        |                 |                |     |
       |        |   ,--> infix1 --|                |     |
       |        |   |    |        |                |     |
       |        |   ,--> infix2 --|                |     |
       v        v   |    |        |                |     |
       prefix -(c)-(+)-> infix3 --'                |     |
                    |    |                         ^     |
                    |    |                         |     |
                    |---------------> suffix1 -->--|     |
                    |    |             ^           |     |
                    |    |             |           |     |
                    |---------------> suffix2 ----{1}------> {exit} --> (c)
                    |    |             ^                 |     |
                    |    |             |                 |     v
                    |    |             |                 |     |
                    |---------------> suffix3 -------------> {exit} --> (c)
                    |    |             ^                 |     |
                    | sets             |                 |     v
                    |    |             maybe             |     |
                    |    |             used              |     |
                    |    |             |                 |     |
                    |    |     infix --'                 |     |
                    |    `---> value                     |     |
                    |           ^                        |     |
                    |           |                        |     |
                    |       hides                        |     |
                    |           |                        |     |
                    |           `--------------------------<---|
                    |                                    |     |
                    `--> any command --{2}-> {warn} -->--|     |
                                        |                |     |
                                        |--> {noop} -->--|     |
                                        |                |     |
                                        |--> {call} -->--'     ^
                                        |                      |
                                        `------------------> {exit} --> (c)
 
    This diagram provides more information about the infix value and also
 takes external state into account.
 
                                             ,----sets--- "anything"
                                             |
                                             v
                            ,---------> external
                            |           state
                            |            | |
                            |  initialized |                      ☉‿⚆
                         sets         from |
                            |            | maybe
                            | ,----------' used
                            | |            |
      (c)                   | |            v
       |        ,- {stay} --|---<-,-<------|-----<-,-<---,
      (+)       |           | |   |        |       |     |
       |        |           | v   |        |       |     |
       |        |   ,--> infix1 --|        |       |     |
       |        |   |       | |   |        |       |     |
       |        |   |       | v   |        |       |     |
       |        |   ,--> infix2 --|        |       |     |
       |        |   |    | ^      |        |       |     |
       v        v   |    | |      |        |       |     |
       prefix -(c)-(+)-> infix3 --'        |       |     |
                    |    | ^               |       ^     |
                    |    | |               v       |     |
                    |---------------> suffix1 -->--|     |
                    |    | |            ^  |       |     |
                    |    | |            |  v       |     |
                    |---------------> suffix2 ----{1}------> {exit} --> (c)
                    |    | |            ^  |             |     |
                    |    | |            |  |             |     v
                    |    | |            |  v             |     |
                    |---------------> suffix3 -------------> {exit} --> (c)
                    |    | |            ^                |     |
                    | sets |            |                |     v
                    |    | initialized  maybe            |     |
                    |    | from         used             |     |
                    |    | |            |                |     |
                    |    | `-- infix ---'                |     |
                    |    `---> value -----------------------------> persistent
                    |           ^ ^                      |     |    across
                    |           | |                      |     |    invocations -,
                    |       hides |                      |     |                 |
                    |           | `----------------------------------------------'
                    |           |                        |     |
                    |           `--------------------------<---|
                    |                                    |     |
                    `--> any command --{2}-> {warn} -->--|     |
                                        |                |     |
                                        |--> {noop} -->--|     |
                                        |                |     |
                                        |--> {call} -->--'     ^
                                        |                      |
                                        `------------------> {exit} --> (c)
 
    • ‘{1}’ Transients can be configured to be exited when a suffix
      command is invoked.  The default is to do so for all suffixes
      except for those that are common to all transients and which are
      used to perform tasks such as providing help and saving the value
      of the infix arguments for future invocations.  The behavior can
      also be specified for individual suffix commands and may even
      depend on state.
 
    • ‘{2}’ Transients can be configured to allow the user to invoke
      non-suffix commands.  The default is to not allow that and instead
      warn the user.
 
    Despite already being rather complex, even the last diagram leaves
 out many details.  Most importantly it implies that the decision whether
 to remain transient is made later than it actually is made (for the most
 part a function on ‘pre-command-hook’ is responsible).  But such
 implementation details are of little relevance to users and are covered
 elsewhere.
 
 
 File: transient.info,  Node: Comparison With Other Packages,  Prev: Comparison With Prefix Keys and Prefix Arguments,  Up: Related Abstractions and Packages
 
 6.2 Comparison With Other Packages
 ==================================
 
 Magit-Popup
 -----------
 
 Transient is the successor to Magit-Popup (see *note
 (magit-popup)Top::).
 
    One major difference between these two implementations of the same
 ideas is that while Transient uses transient keymaps and embraces the
 command-loop, Magit-Popup implemented an inferior mechanism that does
 not use transient keymaps and that instead of using the command-loop
 implements a naive alternative based on ‘read-char’.
 
    Magit-Popup does not use classes and generic functions and defining a
 new command type is near impossible as it involves adding hard-coded
 special-cases to many functions.  Because of that only a single new type
 was added, which was not already part of Magit-Popup’s initial release.
 
    A lot of things are hard-coded in Magit-Popup.  One random example is
 that the key bindings for switches must begin with "-" and those for
 options must begin with "=".
 
 Hydra
 -----
 
 Hydra (see <https://github.com/abo-abo/hydra>) is another package that
 provides features similar to those of Transient.
 
    Both packages use transient keymaps to make a set of commands
 temporarily available and show the available commands in a popup buffer.
 
    A Hydra "body" is equivalent to a Transient "prefix" and a Hydra
 "head" is equivalent to a Transient "suffix".  Hydra has no equivalent
 of a Transient "infix".
 
    Both hydras and transients can be used as simple command dispatchers.
 Used like this they are similar to regular prefix commands and prefix
 keys, except that the available commands are shown in the popup buffer.
 
    (Another package that does this is ‘which-key’.  It does so
 automatically for any incomplete key sequence.  The advantage of that
 approach is that no additional work is necessary; the disadvantage is
 that the available commands are not organized semantically.)
 
    Both Hydra and Transient provide features that go beyond simple
 command dispatchers:
 
    • Invoking a command from a hydra does not necessarily exit the
      hydra.  That makes it possible to invoke the same command again,
      but using a shorter key sequence (i.e.  the key that was used to
      enter the hydra does not have to be pressed again).
 
      Transient supports that too, but for now this feature is not a
      focus and the interface is a bit more complicated.  A very basic
      example using the current interface:
 
           (transient-define-prefix outline-navigate ()
             :transient-suffix     'transient--do-stay
             :transient-non-suffix 'transient--do-warn
             [("p" "previous visible heading" outline-previous-visible-heading)
              ("n" "next visible heading" outline-next-visible-heading)])
 
    • Transient supports infix arguments; values that are set by infix
      commands and then consumed by the invoked suffix command(s).
 
      To my knowledge, Hydra does not support that.
 
    Both packages make it possible to specify how exactly the available
 commands are outlined:
 
    • With Hydra this is often done using an explicit format string,
      which gives authors a lot of flexibility and makes it possible to
      do fancy things.
 
      The downside of this is that it becomes harder for a user to add
      additional commands to an existing hydra and to change key
      bindings.
 
    • Transient allows the author of a transient to organize the commands
      into groups and the use of generic functions allows authors of
      transients to control exactly how a certain command type is
      displayed.
 
      However while Transient supports giving sections a heading it does
      not currently support giving the displayed information more
      structure by, for example, using box-drawing characters.
 
      That could be implemented by defining a new group class, which lets
      the author specify a format string.  It should be possible to
      implement that without modifying any existing code, but it does not
      currently exist.
 
 
 File: transient.info,  Node: FAQ,  Next: Keystroke Index,  Prev: Related Abstractions and Packages,  Up: Top
 
 Appendix A FAQ
 **************
 
 A.1 Can I control how the popup buffer is displayed?
 ====================================================
 
 Yes, see ‘transient-display-buffer-action’ in *note Other Options::.
 
 A.2 Why did some of the key bindings change?
 ============================================
 
 You may have noticed that the bindings for some of the common commands
 do *not* have the prefix ‘C-x’ and that furthermore some of these
 commands are grayed out while others are not.  That unfortunately is a
 bit confusing if the section of common commands is not shown
 permanently, making the following explanation necessary.
 
    The purpose of usually hiding that section but showing it after the
 user pressed the respective prefix key is to conserve space and not
 overwhelm users with too much noise, while allowing the user to quickly
 list common bindings on demand.
 
    That however should not keep us from using the best possible key
 bindings.  The bindings that do use a prefix do so to avoid wasting too
 many non-prefix bindings, keeping them available for use in individual
 transients.  The bindings that do not use a prefix and that are *not*
 grayed out are very important bindings that are *always* available, even
 when invoking the "common command key prefix" or *any other*
 transient-specific prefix.  The non-prefix keys that *are* grayed out
 however, are not available when any incomplete prefix key sequence is
 active.  They do not use the "common command key prefix" because it is
 likely that users want to invoke them several times in a row and e.g.
 ‘M-p M-p M-p’ is much more convenient than ‘C-x M-p C-x M-p C-x M-p’.
 
    You may also have noticed that the "Set" command is bound to ‘C-x s’,
 while Magit-Popup used to bind ‘C-c C-c’ instead.  I have seen several
 users praise the latter binding (sic), so I did not change it
 willy-nilly.  The reason that I changed it is that using different
 prefix keys for different common commands, would have made the temporary
 display of the common commands even more confusing, i.e.  after pressing
 ‘C-c’ all the ‘C-x ...’ bindings would be grayed out.
 
    Using a single prefix for common commands key means that all other
 potential prefix keys can be used for transient-specific commands
 *without* the section of common commands also popping up.  ‘C-c’ in
 particular is a prefix that I want to (and already do) use for Magit,
 and also using that for a common command would prevent me from doing so.
 
    (Also see the next question.)
 
 A.3 Why does ‘q’ not quit popups anymore?
 =========================================
 
 I agree that ‘q’ is a good binding for commands that quit something.
 This includes quitting whatever transient is currently active, but it
 also includes quitting whatever it is that some specific transient is
 controlling.  The transient ‘magit-blame’ for example binds ‘q’ to the
 command that turns ‘magit-blame-mode’ off.
 
    So I had to decide if ‘q’ should quit the active transient (like
 Magit-Popup used to) or whether ‘C-g’ should do that instead, so that
 ‘q’ could be bound in individual transient to whatever commands make
 sense for them.  Because all other letters are already reserved for use
 by individual transients, I have decided to no longer make an exception
 for ‘q’.
 
    If you want to get ‘q’’s old binding back then you can do so.  Doing
 that is a bit more complicated than changing a single key binding, so I
 have implemented a function, ‘transient-bind-q-to-quit’ that makes the
 necessary changes.  See its doc string for more information.
 
 
 File: transient.info,  Node: Keystroke Index,  Next: Command Index,  Prev: FAQ,  Up: Top
 
 Appendix B Keystroke Index
 **************************
 
  * Menu:
 
 * C-g:                                   Aborting and Resuming Transients.
                                                                (line 25)
 * C-g <1>:                               Aborting and Resuming Transients.
                                                                (line 26)
 * C-h:                                   Getting Help for Suffix Commands.
                                                                (line 10)
 * C-M-n:                                 Using History.        (line 17)
 * C-M-p:                                 Using History.        (line 11)
 * C-q:                                   Aborting and Resuming Transients.
                                                                (line 36)
 * C-x C-s:                               Saving Values.        (line 25)
 * C-x l:                                 Enabling and Disabling Suffixes.
                                                                (line 44)
 * C-x n:                                 Using History.        (line 18)
 * C-x p:                                 Using History.        (line 12)
 * C-x s:                                 Saving Values.        (line 20)
 * C-x t:                                 Common Suffix Commands.
                                                                (line 17)
 * C-z:                                   Aborting and Resuming Transients.
                                                                (line 42)
 * M-x transient-resume:                  Aborting and Resuming Transients.
                                                                (line 55)
 
 
 File: transient.info,  Node: Command Index,  Next: Function Index,  Prev: Keystroke Index,  Up: Top
 
 Appendix C Command Index
 ************************
 
  * Menu:
 
 * transient-help:                        Getting Help for Suffix Commands.
                                                                (line 10)
 * transient-history-next:                Using History.        (line 17)
 * transient-history-next <1>:            Using History.        (line 18)
 * transient-history-prev:                Using History.        (line 11)
 * transient-history-prev <1>:            Using History.        (line 12)
 * transient-quit-all:                    Aborting and Resuming Transients.
                                                                (line 36)
 * transient-quit-one:                    Aborting and Resuming Transients.
                                                                (line 26)
 * transient-quit-seq:                    Aborting and Resuming Transients.
                                                                (line 25)
 * transient-resume:                      Aborting and Resuming Transients.
                                                                (line 55)
 * transient-save:                        Saving Values.        (line 25)
 * transient-scroll-down arg:             Other Commands.       (line 18)
 * transient-scroll-up arg:               Other Commands.       (line 12)
 * transient-set:                         Saving Values.        (line 20)
 * transient-set-level:                   Enabling and Disabling Suffixes.
                                                                (line 44)
 * transient-suspend:                     Aborting and Resuming Transients.
                                                                (line 42)
 * transient-toggle-common:               Common Suffix Commands.
                                                                (line 17)
 
 
 File: transient.info,  Node: Function Index,  Next: Variable Index,  Prev: Command Index,  Up: Top
 
 Appendix D Function Index
 *************************
 
  * Menu:
 
 * transient--do-call:                    Transient State.     (line  98)
 * transient--do-exit:                    Transient State.     (line  94)
 * transient--do-noop:                    Transient State.     (line 125)
 * transient--do-quit-all:                Transient State.     (line 138)
 * transient--do-quit-one:                Transient State.     (line 132)
 * transient--do-replace:                 Transient State.     (line 102)
 * transient--do-stay:                    Transient State.     (line  85)
 * transient--do-suspend:                 Transient State.     (line 144)
 * transient--do-warn:                    Transient State.     (line 121)
 * transient--history-init:               Prefix Classes.      (line  10)
 * transient--insert-group:               Group Methods.       (line  20)
 * transient-append-suffix:               Modifying Existing Transients.
                                                               (line  47)
 * transient-arg-value:                   Using Infix Arguments.
                                                               (line  32)
 * transient-args:                        Using Infix Arguments.
                                                               (line  22)
 * transient-define-argument:             Defining Suffix and Infix Commands.
                                                               (line  63)
 * transient-define-infix:                Defining Suffix and Infix Commands.
                                                               (line  27)
 * transient-define-prefix:               Defining Transients. (line  13)
 * transient-define-suffix:               Defining Suffix and Infix Commands.
                                                               (line   9)
 * transient-format:                      Suffix Format Methods.
                                                               (line   6)
 * transient-format-description:          Suffix Format Methods.
                                                               (line  20)
 * transient-format-key:                  Suffix Format Methods.
                                                               (line  15)
 * transient-format-value:                Suffix Format Methods.
                                                               (line  25)
 * transient-get-suffix:                  Modifying Existing Transients.
                                                               (line  60)
 * transient-infix-read:                  Suffix Value Methods.
                                                               (line  17)
 * transient-infix-set:                   Suffix Value Methods.
                                                               (line  39)
 * transient-infix-value:                 Suffix Value Methods.
                                                               (line  43)
 * transient-init-scope:                  Suffix Value Methods.
                                                               (line  57)
 * transient-init-value:                  Suffix Value Methods.
                                                               (line   6)
 * transient-insert-suffix:               Modifying Existing Transients.
                                                               (line  42)
 * transient-prompt:                      Suffix Value Methods.
                                                               (line  34)
 * transient-remove-suffix:               Modifying Existing Transients.
                                                               (line  56)
 * transient-replace-suffix:              Modifying Existing Transients.
                                                               (line  51)
 * transient-scroll-down:                 Other Commands.      (line  18)
 * transient-scroll-up:                   Other Commands.      (line  12)
 * transient-setup-children:              Group Methods.       (line   6)
 * transient-show-help:                   Suffix Format Methods.
                                                               (line  30)
 * transient-suffix-put:                  Modifying Existing Transients.
                                                               (line  65)
 * transient-suffixes:                    Using Infix Arguments.
                                                               (line  40)
 
 
 File: transient.info,  Node: Variable Index,  Prev: Function Index,  Up: Top
 
 Appendix E Variable Index
 *************************
 
  * Menu:
 
 * transient-current-command:             Using Infix Arguments.
                                                               (line  62)
 * transient-current-prefix:              Using Infix Arguments.
                                                               (line  56)
 * transient-current-suffixes:            Using Infix Arguments.
                                                               (line  47)
 * transient-default-level:               Enabling and Disabling Suffixes.
                                                               (line  33)
 * transient-detect-key-conflicts:        Other Options.       (line 151)
 * transient-display-buffer-action:       Other Options.       (line  46)
 * transient-enable-popup-navigation:     Other Options.       (line  28)
 * transient-force-fixed-pitch:           Other Options.       (line 165)
 * transient-highlight-mismatched-keys:   Other Options.       (line 110)
 * transient-history-file:                Using History.       (line  35)
 * transient-history-limit:               Using History.       (line  40)
 * transient-levels-file:                 Enabling and Disabling Suffixes.
                                                               (line  39)
 * transient-mode-line-format:            Other Options.       (line  85)
 * transient-read-with-initial-input:     Other Options.       (line 102)
 * transient-show-common-commands:        Common Suffix Commands.
                                                               (line  24)
 * transient-show-popup:                  Other Options.       (line   6)
 * transient-substitute-key-function:     Other Options.       (line 129)
 * transient-values-file:                 Saving Values.       (line  30)
 
 
 
 Tag Table:
 Node: Top751
 Node: Introduction3651
 Node: Usage9466
 Node: Invoking Transients9834
 Node: Aborting and Resuming Transients10911
 Node: Common Suffix Commands13570
 Node: Saving Values15404
 Ref: Saving Values-Footnote-116662
 Node: Using History16855
 Node: Getting Help for Suffix Commands18494
 Node: Enabling and Disabling Suffixes19887
 Node: Other Commands22925
 Node: Other Options23903
 Node: Modifying Existing Transients31617
 Node: Defining New Commands35011
 Node: Defining Transients35347
 Node: Binding Suffix and Infix Commands37778
 Node: Group Specifications38632
 Node: Suffix Specifications42961
 Node: Defining Suffix and Infix Commands47326
 Node: Using Infix Arguments50524
 Node: Transient State53356
 Ref: Pre-commands for Infixes57264
 Ref: Pre-commands for Suffixes57536
 Ref: Pre-commands for Non-Suffixes58055
 Ref: Special Pre-Commands58670
 Node: Classes and Methods59181
 Node: Group Classes61395
 Node: Group Methods63311
 Node: Prefix Classes64560
 Node: Suffix Classes65652
 Node: Suffix Methods67896
 Node: Suffix Value Methods68217
 Node: Suffix Format Methods70977
 Node: Prefix Slots72429
 Ref: Internal Prefix Slots73687
 Node: Suffix Slots74944
 Ref: Slots of transient-suffix75312
 Ref: Slots of transient-infix76009
 Ref: Slots of transient-variable77957
 Ref: Slots of transient-switches78059
 Node: Predicate Slots78422
 Node: Related Abstractions and Packages79670
 Node: Comparison With Prefix Keys and Prefix Arguments79957
 Ref: Regular Prefix Commands80645
 Ref: Regular Prefix Arguments80993
 Ref: Transients81962
 Node: Comparison With Other Packages90233
 Ref: Magit-Popup90464
 Ref: Hydra91363
 Node: FAQ94399
 Ref: Can I control how the popup buffer is displayed?94542
 Ref: Why did some of the key bindings change?94723
 Ref: Why does q not quit popups anymore?97040
 Node: Keystroke Index98133
 Node: Command Index99913
 Node: Function Index101846
 Node: Variable Index106350
 
 End Tag Table
 
 
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