dotemacs

transient.org (90907B)

---

 #+title: Transient User and Developer Manual
 :PREAMBLE:
 #+author: Jonas Bernoulli
 #+email: jonas@bernoul.li
 #+date: 2018-{{{year}}}
 
 #+texinfo_dir_category: Emacs misc features
 #+texinfo_dir_title: Transient: (transient).
 #+texinfo_dir_desc: Transient Commands
 #+subtitle: for version 0.6.0
 
 #+setupfile: .orgconfig
 
 Transient is the library used to implement the keyboard-driven “menus”
 in Magit.  It is distributed as a separate package, so that it can be
 used to implement similar menus in other packages.
 
 This manual can be bit hard to digest when getting started.  A useful
 resource to get over that hurdle is Psionic K's interactive tutorial,
 available at https://github.com/positron-solutions/transient-showcase.
 
 #+texinfo: @noindent
 This manual is for Transient version 0.6.0.
 
 #+texinfo: @insertcopying
 :END:
 * Introduction
 
 Transient is the library used to implement the keyboard-driven {{{dfn(menus)}}}
 in Magit.  It is distributed as a separate package, so that it can be
 used to implement similar menus in other packages.
 
 This manual can be bit hard to digest when getting started.  A useful
 resource to get over that hurdle is Psionic K's interactive tutorial,
 available at https://github.com/positron-solutions/transient-showcase.
 
 ** Some things that Transient can do
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 - Display current state of arguments
 - Display and manage lifecycle of modal bindings
 - Contextual user interface
 - Flow control for wizard-like composition of interactive forms
 - History & persistence
 - Rendering arguments for controlling CLI programs
 
 ** Complexity in CLI programs
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 Complexity tends to grow with time.  How do you manage the complexity
 of commands?  Consider the humble shell command =ls=.  It now has over
 /fifty/ command line options.  Some of these are boolean flags (=ls -l=).
 Some take arguments (=ls --sort=s=).  Some have no effect unless paired
 with other flags (=ls -lh=).  Some are mutually exclusive.  Some shell
 commands even have so many options that they introduce /subcommands/
 (=git branch=, =git commit=), each with their own rich set of options
 (=git branch -f=).
 
 ** Using Transient for composing interactive commands
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 What about Emacs commands used interactively? How do these handle
 options?  One solution is to make many versions of the same command,
 so you don't need to! Consider: =delete-other-windows= vs.
 =delete-other-windows-vertically= (among many similar examples).
 
 Some Emacs commands will simply prompt you for the next "argument"
 (=M-x switch-to-buffer=).  Another common solution is to use prefix
 arguments which usually start with =C-u=.  Sometimes these are sensibly
 numerical in nature (=C-u 4 M-x forward-paragraph= to move forward 4
 paragraphs).  But sometimes they function instead as boolean
 "switches" (=C-u C-SPACE= to jump to the last mark instead of just
 setting it, =C-u C-u C-SPACE= to unconditionally set the mark).  Since
 there aren't many standards for the use of prefix options, you have to
 read the command's documentation to find out what the possibilities
 are.
 
 But when an Emacs command grows to have a truly large set of options
 and arguments, with dependencies between them, lots of option values,
 etc., these simple approaches just don't scale.  Transient is designed
 to solve this issue.  Think of it as the humble prefix argument =C-u=,
 /raised to the power of 10/.  Like =C-u=, it is key driven.  Like the
 shell, it supports boolean "flag" options, options that take
 arguments, and even "sub-commands", with their own options.  But
 instead of searching through a man page or command documentation,
 well-designed transients /guide/ their users to the relevant set of
 options (and even their possible values!) directly, taking into
 account any important pre-existing Emacs settings.  And while for
 shell commands like =ls=, there is only one way to "execute" (hit
 =Return=!), transients can "execute" using multiple different keys tied
 to one of many self-documenting /actions/ (imagine having 5 different
 colored return keys on your keyboard!).  Transients make navigating
 and setting large, complex groups of command options and arguments
 easy.  Fun even.  Once you've tried it, it's hard to go back to the
 =C-u what can I do here again?= way.
 
 * Usage
 ** Invoking Transients
 #+cindex: 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.
 
 ** Aborting and Resuming Transients
 #+cindex: aborting transients
 #+cindex: resuming transients
 
 #+cindex: quit transient
 To quit the transient without invoking a suffix command press {{{kbd(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 {{{kbd(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 {{{kbd(C-g)}}} while a nested transient is active only
 quits the innermost transient, causing a return to the previous
 transient.
 
 {{{kbd(C-q)}}} or {{{kbd(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
 {{{kbd(M-x transient-resume)}}}.
 
 #+attr_texinfo: :compact t
 - Key: C-g (transient-quit-seq) ::
 - Key: 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,
   it returns to the previous transient, if any.
 
 Transient's predecessor bound {{{kbd(q)}}} instead of {{{kbd(C-g)}}} to the quit command.
 To learn how to get that binding back see ~transient-bind-q-to-quit~'s
 documentation string.
 
 - Key: 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.
 
 - Key: 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.
 
 - Key: M-x transient-resume ::
 
   This command resumes the previously suspended stack of transients,
   if any.
 
 ** Common Suffix Commands
 #+cindex: 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 section,
 as well as some other commands that are all bound to {{{kbdvar(C-x <KEY>)}}}.  After
 {{{kbd(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.
 
 - Key: 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 {{{kbd(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 too many options.
 
   While a transient is active, pressing {{{kbd(C-x)}}} always shows the common
   commands.  The value of this option can be changed for the current
   Emacs session by typing {{{kbd(C-x t)}}} while a transient is active.
 
 The other common commands are described in either the previous or in
 one of the following sections.
 
 Some of Transient's key bindings differ from the respective bindings
 of Magit-Popup; see [[*FAQ]] for more information.
 
 ** Saving Values
 #+cindex: saving values of arguments
 
 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. [fn: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 [[*Using History]]).
 
 - Key: C-x s (transient-set) ::
 
   This command saves the value of the active transient for this Emacs
   session.
 
 - Key: C-x C-s (transient-save) ::
 
   Save the value of the active transient persistently across Emacs
   sessions.
 
 - Key: C-x C-k (transient-reset) ::
 
   Clear the set and saved values of the active transient.
 
 - User Option: transient-values-file ::
 
   This option names the file that is used to persist the values of
   transients between Emacs sessions.
 
 [fn: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.
 
 ** Using History
 #+cindex: value 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.
 
 #+attr_texinfo: :compact t
 - Key: C-M-p (transient-history-prev) ::
 - Key: C-x p ::
 
   This command switches to the previous value used for the active
   transient.
 
 - Key: C-M-n (transient-history-next) ::
 - Key: C-x n ::
 
   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, 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
 [[*Suffix Slots]]).
 
 Both kinds of history are saved to a file when Emacs is exited.
 
 - User Option: transient-history-file ::
 
   This option names the file that 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~.
 
 ** Getting Help for Suffix Commands
 #+cindex: getting help
 
 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.
 
 - Key: C-h (transient-help) ::
 
   This command enters help mode.  When help mode is active, typing a
   key shows information about the suffix command that the key normally
   is bound to (instead of invoking it).  Pressing {{{kbd(C-h)}}} a second time
   shows information about the /prefix/ command.
 
   After typing a key, the stack of transient states is suspended and
   information about the suffix command is shown instead.  Typing {{{kbd(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 documentation
 string, for non-infix suffixes this is usually appropriate.
 
 ** Enabling and Disabling Suffixes
 #+cindex: enabling suffixes
 #+cindex: 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.
 
 #+cindex: levels
 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 {{{dfn(levels)}}} to describe that mechanism.
 
 #+cindex: transient-level
 Each suffix command is placed on a level and each transient has a
 level (called {{{dfn(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 {{{kbd(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 option names the file that is used to persist the levels of
   transients and their suffixes between Emacs sessions.
 
 - Key: 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 {{{kbd(C-x l)}}} again.
 
   To exit edit mode press {{{kbd(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.
 
 - Key: C-x a (transient-toggle-level-limit) ::
 
   This command toggle whether suffixes that are on levels higher than
   the level specified by ~transient-default-level~ are temporarily
   available anyway.
 
 ** 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 {{{var(ARG)}}}
   lines.  If {{{var(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 {{{var(ARG)}}}
   lines.  If {{{var(ARG)}}} is ~nil~, then it scrolls near full screen.  This
   is a wrapper around ~scroll-down-command~ (which see).
 
 ** Configuration
 
 More options are described in [[* Common Suffix Commands]], in [[* Saving
 Values]], in [[* Using History]] and in [[* Enabling and Disabling Suffixes]].
 
 *** Essential Options
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 Also see [[* Common Suffix Commands]].
 
 - 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,
     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:
 
   - {{{kbd(UP)}}} moves the cursor to the previous suffix.
   - {{{kbd(DOWN)}}} moves the cursor to the next suffix.
   - {{{kbd(RET)}}} invokes the suffix the cursor is on.
   - {{{kbd(mouse-1)}}} invokes the clicked on suffix.
   - {{{kbd(C-s)}}} and {{{kbd(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
   {{{codevar((display-buffer BUFFER transient-display-buffer-action))}}}.
 
   The value of this option has the form {{{codevar((FUNCTION . ALIST))}}},
   where {{{var(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 {{{var(ALIST)}}}.  See [[info:elisp#Choosing Window]],
   for details.
 
   The default is:
 
   #+BEGIN_SRC emacs-lisp
     (display-buffer-in-side-window
       (side . bottom)
       (inhibit-same-window . t)
       (window-parameters (no-other-window . t)))
   #+END_SRC
 
   This displays the window at the bottom of the selected frame.
   Another useful {{{var(FUNCTION)}}} is ~display-buffer-below-selected~, which
   is what ~magit-popup~ used by default.  For more alternatives see
   [[info:elisp#Buffer Display Action Functions]], and [[info: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~.
 
 *** Accessibility Options
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 - User Option: transient-force-single-column ::
 
   This option controls whether the use of a single column to display
   suffixes is enforced.  This might be useful for users with low
   vision who use large text and might otherwise have to scroll in two
   dimensions.
 
 *** Auxiliary Options
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 - 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) or a natural number, then the buffer
   has no mode-line, but a line is drawn is drawn in its place.
   If a number is used, that specifies the thickness of the line.
   On termcap frames we cannot draw lines, so there ~line~ and
   numbers are synonyms for ~nil~.
 
   The color of the line is used to indicate if non-suffixes are
   allowed and whether they exit the transient.  The foreground
   color of ~transient-key-noop~ (if non-suffix are disallowed),
   ~transient-key-stay~ (if allowed and transient stays active), or
   ~transient-key-exit~ (if allowed and they exit the transient) is
   used to draw the line.
 
   Otherwise this can be any mode-line format.  See [[info:elisp#Mode
   Line Format]], for details.
 
 - User Option: transient-semantic-coloring ::
 
   This option controls whether colors are used to indicate the
   transient behavior of commands.
 
   If non-~nil~, then the key binding of each suffix is colorized to
   indicate whether it exits the transient state or not.  The color of
   the prefix is indicated using the line that is drawn when the value
   of ~transient-mode-line-format~ is ~line~.
 
 - 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~, 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, {{{kbd(=)}}} is hard to reach using my custom keyboard layout,
   so I substitute {{{kbd(()}}} for that, which is easy to reach using a layout
   optimized for lisp.
 
   #+BEGIN_SRC emacs-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))))
   #+END_SRC
 
 - 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~, there is no initial input and the first
   element has to be accessed the same way as the older elements.
 
 - User Option: transient-hide-during-minibuffer-read ::
 
   This option controls whether the transient buffer is hidden while
   user input is being read in the minibuffer.
 
 - User Option: transient-align-variable-pitch ::
 
   This option controls whether columns are aligned pixel-wise in the
   popup buffer.
 
   If this is non-~nil~, then columns are aligned pixel-wise to support
   variable-pitch fonts.  Keys are not aligned, so you should use a
   fixed-pitch font for the ~transient-key~ face.  Other key faces
   inherit from that face unless a theme is used that breaks that
   relationship.
 
   This option is intended for users who use a variable-pitch font for
   the ~default~ face.
 
 - 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.
 
 *** Developer Options
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 These options are mainly intended for developers.
 
 - 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, 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-highlight-higher-levels ::
 
   This option controls whether suffixes that would not be available by
   default are highlighted.
 
   When non-~nil~ then the descriptions of suffixes are highlighted if
   their level is above 4, the default of ~transient-default-level~.
   Assuming you have set that variable to 7, this highlights all
   suffixes that won't be available to users without them making the
   same customization.
 
 * Modifying Existing Transients
 #+cindex: modifying existing transients
 
 To an extent, transients can be customized interactively, see
 [[*Enabling and Disabling Suffixes]].  This section explains how existing
 transients can be further modified non-interactively.  Let's begin
 with an example:
 
 #+begin_src emacs-lisp
   (transient-append-suffix 'magit-patch-apply "-3"
     '("-R" "Apply in reverse" "--reverse"))
 #+end_src
 
 This inserts a new infix argument to toggle the ~--reverse~ argument
 after the infix argument that toggles ~-3~ in ~magit-patch-apply~.
 
 The following functions share a few arguments:
 
 - {{{var(PREFIX)}}} is a transient prefix command, a symbol.
 
 - {{{var(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 [[*Suffix Specifications]].
 
   {{{var(SUFFIX)}}} may also be a group in the same form as expected by
   ~transient-define-prefix~.  See [[*Group Specifications]].
 
 - {{{var(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 {{{var(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 {{{var(PREFIX)}}} symbol.  Suffix entries in
 that tree are not objects but have the form {{{codevar((LEVEL CLASS PLIST))}}}, where
 {{{var(PLIST)}}} should set at least ~:key~, ~:description~ and ~:command~.
 
 - Function: transient-insert-suffix prefix loc suffix &optional keep-other ::
 - Function: transient-append-suffix prefix loc suffix &optional keep-other ::
 
   These functions insert the suffix or group {{{var(SUFFIX)}}} into {{{var(PREFIX)}}} before
   or after {{{var(LOC)}}}.
 
   Conceptually adding a binding to a transient prefix is similar to
   adding a binding to a keymap, but this is complicated by the fact
   that multiple suffix commands can be bound to the same key, provided
   they are never active at the same time, see [[*Predicate Slots]].
 
   Unfortunately both false-positives and false-negatives are possible.
   To deal with the former use non-~nil~ {{{var(KEEP-OTHER.)}}}  To deal with the
   latter remove the conflicting binding explicitly.
 
 - Function: transient-replace-suffix prefix loc suffix ::
 
   This function replaces the suffix or group at {{{var(LOC)}}} in {{{var(PREFIX)}}} with
   suffix or group {{{var(SUFFIX)}}}.
 
 - Function: transient-remove-suffix prefix loc ::
 
   This function removes the suffix or group at {{{var(LOC)}}} in {{{var(PREFIX)}}}.
 
 - Function: transient-get-suffix prefix loc ::
 
   This function returns the suffix or group at {{{var(LOC)}}} in {{{var(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 {{{var(LOC)}}} in {{{var(PREFIX)}}}, by setting
   the {{{var(PROP)}}} of its plist to {{{var(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 {{{var(LOC)}}} cannot be found in {{{var(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.
 
 * Defining New Commands
 ** Technical Introduction
 
 Taking inspiration from prefix keys and prefix arguments, Transient
 implements a similar abstraction involving a prefix command, infix
 arguments and suffix commands.
 
 When the user calls a transient prefix command, 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~.
 
 #+cindex: command dispatchers
 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, which can be thought of as a “menus”.  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 {{{kbd(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, one can call a command with arguments that are
 just as complex as when calling the same function non-interactively
 from Lisp.
 
 Invoking a transient suffix 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 [[*Using History]].
 
 After a transient prefix command is invoked, {{{kbdvar(C-h <KEY>)}}} can be used to
 show the documentation for the infix or suffix command that {{{kbdvar(<KEY>)}}} is
 bound to (see [[*Getting Help for Suffix Commands]]), and infixes and
 suffixes can be removed from the transient using {{{kbdvar(C-x l <KEY>)}}}. Infixes
 and suffixes that are disabled by default can be enabled the same way.
 See [[*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).
 
 Note that suffix commands also support regular prefix arguments.  A
 suffix command may even be called with both infix and prefix arguments
 at the same time.  If you invoke a command as a suffix of a transient
 prefix command, but also want to pass prefix arguments to it, then
 first invoke the prefix command, and only after doing that invoke the
 prefix arguments, before finally invoking the suffix command.  If you
 instead began by providing the prefix arguments, then those would
 apply to the prefix command, not the suffix command.  Likewise, if you
 want to change infix arguments before invoking a suffix command with
 prefix arguments, then change the infix arguments before invoking the
 prefix arguments.  In other words, regular prefix arguments always
 apply to the next command, and since transient prefix, infix and
 suffix commands are just regular commands, the same applies to them.
 (Regular prefix keys behave differently because they are not commands
 at all, instead they are just incomplete key sequences, and those
 cannot be interrupted with prefix commands.)
 
 ** 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 {{{var(NAME)}}} as a transient prefix command and binds the
   transient's infix and suffix commands.
 
   {{{var(ARGLIST)}}} are the arguments that the prefix command takes.
   {{{var(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.
 
   {{{var(GROUP)}}}s add key bindings for infix and suffix commands and specify
   how these bindings are presented in the popup buffer.  At least one
   {{{var(GROUP)}}} has to be specified.  See [[*Binding Suffix and Infix Commands]].
 
   The {{{var(BODY)}}} is optional.  If it is omitted, then {{{var(ARGLIST)}}} is ignored and
   the function definition becomes:
 
   #+BEGIN_SRC emacs-lisp
     (lambda ()
       (interactive)
       (transient-setup 'NAME))
   #+END_SRC
 
   If {{{var(BODY)}}} is specified, then it must begin with an ~interactive~ form
   that matches {{{var(ARGLIST)}}}, and it must call ~transient-setup~.  It may,
   however, call that function only when some condition is satisfied.
 
   #+cindex: scope of a transient
   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:
 
   #+BEGIN_SRC emacs-lisp
     (transient-setup 'NAME nil nil :scope SCOPE)
   #+END_SRC
 
   For example, the scope of the ~magit-branch-configure~ transient is
   the branch whose variables are being configured.
 
 ** Binding Suffix and Infix Commands
 
 The macro ~transient-define-prefix~ is used to define a transient.
 This defines the actual transient prefix command (see [[*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 [[*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~.
 
 *** Group Specifications
 #+cindex: 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 [[*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:
 
 #+begin_src emacs-lisp
   [{LEVEL} {DESCRIPTION} {KEYWORD VALUE}... ELEMENT...]
 #+end_src
 
 The {{{var(LEVEL)}}} is optional and defaults to 4.  See [[*Enabling and Disabling
 Suffixes]].
 
 The {{{var(DESCRIPTION)}}} is optional.  If present, it is used as the heading of
 the group.
 
 The {{{var(KEYWORD)}}}-{{{var(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
   {{{var(DESCRIPTION)}}} at the very beginning of the vector.  The recommendation
   is to use ~:description~ if some other keyword is also used, for
   consistency, or {{{var(DESCRIPTION)}}} otherwise, because it looks better.
 
 - Likewise ~:level~ is equivalent to {{{var(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 [[*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:
 
   #+BEGIN_SRC emacs-lisp
     (lambda ()
       (eq (car transient--redisplay-key)
           ?\C-c)) ; the prefix key shared by all bindings
   #+END_SRC
 
 - The value of ~:setup-children~, if non-~nil~, is a function that takes
   one argument, a potentially list of children, and must return a list
   of children or an empty list.  This can either be used to somehow
   transform the group's children that were defined the normal way, or
   to dynamically create the children from scratch.
 
   The returned children must have the same form as stored in the
   prefix's ~transient--layout~ property, but it is often more convenient
   to use the same form as understood by ~transient-define-prefix~,
   described below.  If you use the latter approach, you can use the
   ~transient-parse-suffixes~ and ~transient-parse-suffix~ functions to
   transform them from the convenient to the expected form.
 
   If you explicitly specify children and then transform them using
   ~:setup-chilren~, then the class of the group is determined as usual,
   based on explicitly specified children.
 
   If you do not explicitly specify children and thus rely solely on
   ~:setup-children~, then you must specify the class using ~:class~.
   For backward compatibility, if you fail to do so, ~transient-column~
   is used and a warning is displayed.  This warning will eventually
   be replaced with an error.
 
 - The boolean ~:pad-keys~ argument controls whether keys of all suffixes
   contained in a group are right padded, effectively aligning the
   descriptions.
 
 The {{{var(ELEMENT)}}}s are either all subgroups, or all suffixes 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 {{{var(ELEMENT)}}}s are not subgroups, then they can be a mixture of
 lists, which specify commands, and strings.  Strings are inserted
 verbatim into the buffer.  The empty string can be used to insert gaps
 between suffixes, which is particularly useful if the suffixes are
 outlined as a table.
 
 Inside group specifications, including inside contained suffix
 specifications, nothing has to be quoted and quoting anyway is
 invalid.  The value following a keyword, can be explicitly unquoted
 using ~,~.  This feature is experimental and should be avoided.
 
 The form of suffix specifications is documented in the next node.
 
 *** Suffix Specifications
 #+cindex: suffix specifications
 
 A transient's suffix and infix commands are bound when the transient
 prefix command is defined using ~transient-define-prefix~, see
 [[*Defining Transients]].  The commands are organized into groups, see
 [[*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 [[*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:
 
 #+begin_src emacs-lisp
   ([LEVEL] [KEY [DESCRIPTION]] COMMAND|ARGUMENT [KEYWORD VALUE]...)
 #+end_src
 
 {{{var(LEVEL)}}}, {{{var(KEY)}}} and {{{var(DESCRIPTION)}}} can also be specified using the {{{var(KEYWORD)}}}s
 ~:level~, ~:key~ and ~:description~.  If the object that is associated with
 {{{var(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.
 
 - {{{var(LEVEL)}}} is the suffix level, an integer between 1 and 7.  See
   [[*Enabling and Disabling Suffixes]].
 
 - {{{var(KEY)}}} is the key binding, either a vector or key description string.
 
 - {{{var(DESCRIPTION)}}} is the description, either a string or a function that
   takes zero or one arguments (the suffix object) and 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.
 
 - {{{var(COMMAND)}}} should be 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).
 
   COMMAND can also be a ~lambda~ expression.
 
   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 {{{var(KEY)}}} and the {{{var(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:
 
   #+BEGIN_SRC emacs-lisp
     (transient-insert-suffix 'some-prefix "k"
       '("!" "Ceci n'est pas une commande" no-command
         :if (lambda () (featurep 'no-library))))
   #+END_SRC
 
   Instead of ~featurep~ you could also use ~require~ with a non-~nil~ value
   for {{{var(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 {{{var(KEYWORD)}}}-{{{var(VALUE)}}} pairs.
 Each keyword has to be a keyword symbol, either ~:class~ or a keyword
 argument supported by the constructor of that class.  See [[*Suffix
 Slots]].
 
 ** Defining Suffix and Infix Commands
 #+cindex: defining suffix commands
 #+cindex: defining 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 {{{var(NAME)}}} as a transient suffix command.
 
   {{{var(ARGLIST)}}} are the arguments that the command takes.
   {{{var(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 {{{var(BODY)}}} must begin with an ~interactive~ form that matches {{{var(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 {{{var(NAME)}}} as a transient infix command.
 
   {{{var(ARGLIST)}}} is always ignored (but mandatory never-the-less) and
   reserved for future use.  {{{var(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:
 
   #+BEGIN_SRC emacs-lisp
     (lambda ()
       (interactive)
       (let ((obj (transient-suffix-object)))
         (transient-infix-set obj (transient-infix-read obj)))
       (transient--show))
   #+END_SRC
 
   ~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-define-suffix~ 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 {{{var(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.
 
 ** Using Infix Arguments
 
 The functions 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
   {{{var(PREFIX)}}}.
 
   If the current command was invoked from the transient prefix command
   {{{var(PREFIX)}}}, then it returns the active infix arguments.  If the current
   command was not invoked from {{{var(PREFIX)}}}, then it returns the set, saved
   or default value for {{{var(PREFIX)}}}.
 
 - Function: transient-arg-value arg args ::
 
   This function return the value of {{{var(ARG)}}} as it appears in {{{var(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 {{{var(ARGS)}}}.
 
 - Function: transient-suffixes prefix ::
 
   This function returns the suffixes of the transient prefix command
   {{{var(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 {{{var(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.
 
 ** Transient State
 #+cindex: 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.
 
 The behavior can be changed for all suffixes of a particular prefix
 and/or for individual suffixes.  The values should nearly always be
 booleans, but certain functions, called “pre-commands”, can also be
 used.  These functions are named ~transient--do-VERB~, and the symbol
 ~VERB~ can be used as a shorthand.
 
 A boolean is interpreted as answering the question "does the
 transient stay active, when this command is invoked?"  ~t~ means that
 the transient stays active, while ~nil~ means that invoking the command
 exits the transient.
 
 Note that when the suffix is a “sub-prefix”, invoking that command
 always activates that sub-prefix, causing the outer prefix to no
 longer be active and displayed.  Here ~t~ means that when you exit the
 inner prefix, then the outer prefix becomes active again, while ~nil~
 means that all outer prefixes are exited at once.
 
 - The behavior for non-suffixes can be set for a particular prefix,
   by the prefix's ~transient-non-suffix~ slot to a boolean, a suitable
   pre-command function, or a shorthand for such a function.  See
   [[*Pre-commands for Non-Suffixes]].
 
 - The common behavior for the suffixes of a particular prefix can be
   set using the prefix's ~transient-suffixes~ slot.
 
   The value specified in this slot does *not* affect infixes.  Because
   it affects both regular suffixes as well as sub-prefixes, which
   have different needs, it is best to avoid explicitly specifying a
   function.
 
 - The behavior of an individual suffix can be changed using its
   ~transient~ slot.  While it is usually best to use a boolean, for this
   slot it can occasionally make sense to specify a function explicitly.
 
   Note that this slot can be set when defining a suffix command using
   ~transient-define-suffix~ and/or in the definition of the prefix.  If
   set in both places, then the latter takes precedence, as usual.
 
 The available pre-command functions are documented in the following
 sub-sections.  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~.
 
 For completeness sake, some notes about complications:
 
 - 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 prefix's ~transient-suffix~ slot, but not
   the suffix's ~transient~ slot.
 
 - While a sub-prefix is active we nearly always want {{{kbd(C-g)}}} to take the
   user back to the “super-prefix”, even when the other suffixes don't
   do that.  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 ~nil~ and the slot being unbound
   are treated as 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.
 
 *** Pre-commands for Infixes
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 The default for infixes is ~transient--do-stay~.  This is also the only
 function that makes sense for infixes, which is why this predicate is
 used even if the value of the prefix's ~transient-suffix~ slot is ~t~.  In
 extremely rare cases, one might want to use something else, which can
 be done by setting the infix's ~transient~ slot directly.
 
 - Function: transient--do-stay ::
 
   Call the command without exporting variables and stay transient.
 
 *** Pre-commands for Suffixes
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 By default, invoking a suffix causes the transient to be exited.
 
 The behavior for an individual suffix command can be changed by
 setting its ~transient~ slot to a boolean (which is highly recommended),
 or to one of the following pre-commands.
 
 - Function: transient--do-exit ::
 
   Call the command after exporting variables and exit the transient.
 
 - Function: transient--do-return ::
 
   Call the command after exporting variables and return to the parent
   prefix.  If there is no parent prefix, then call ~transient--do-exit~.
 
 - Function: transient--do-call ::
 
   Call the command after exporting variables and stay transient.
 
 The following pre-commands are only suitable for sub-prefixes.  It is
 not necessary to explicitly use these predicates because the correct
 predicate is automatically picked based on the value of the ~transient~
 slot for the sub-prefix itself.
 
 - Function: transient--do-recurse ::
 
   Call the transient prefix command, preparing for return to active
   transient.
 
   Whether we actually return to the parent transient is ultimately
   under the control of each invoked suffix.  The difference between
   this pre-command and ~transient--do-stack~ is that it changes the
   value of the ~transient-suffix~ slot to ~t~.
 
   If there is no parent transient, then only call this command and
   skip the second step.
 
 - Function: transient--do-stack ::
 
   Call the transient prefix command, stacking the active transient.
   Push the active transient to the transient stack.
 
   Unless ~transient--do-recurse~ is explicitly used, this pre-command
   is automatically used for suffixes that are prefixes themselves,
   i.e., for sub-prefixes.
 
 - Function: transient--do-replace ::
 
   Call the transient prefix command, replacing the active transient.
   Do not push the active transient to the transient stack.
 
   Unless ~transient--do-recurse~ is explicitly used, this pre-command
   is automatically used for suffixes that are prefixes themselves,
   i.e., for sub-prefixes.
 
 - Function: transient--do-suspend ::
 
   Suspend the active transient, saving the transient stack.
 
   This is used by the command ~transient-suspend~ and optionally also by
   “external events” such as ~handle-switch-frame~.  Such bindings should
   be added to ~transient-predicate-map~.
 
 *** Pre-commands for Non-Suffixes
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 By default, non-suffixes (commands that are bound in other keymaps
 beside the transient keymap) cannot be invoked.  Trying to invoke
 such a command results in a warning and the transient stays active.
 
 If you want a different behavior, then set the ~transient-non-suffix~
 slot of the transient prefix command.  The value should be a boolean,
 answering the question, "is it allowed to invoke non-suffix commands?,
 a pre-command function, or a shorthand for such a function.
 
 If the value is ~t~, then non-suffixes can be invoked, when it is ~nil~
 (the default) then they cannot be invoked.
 
 The only other recommended value is ~leave~.  If that is used, then
 non-suffixes can be invoked, but if one is invoked, then that exits
 the transient.
 
 - Function: transient--do-warn ::
 
   Call ~transient-undefined~ and stay transient.
 
 - Function: transient--do-stay ::
 
   Call the command without exporting variables and stay transient.
 
 - Function: transient--do-leave ::
 
   Call the command without exporting variables and exit the transient.
 
 # transient--do-noop intentionally left undocumented.
 
 *** Special Pre-Commands
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 - Function: transient--do-quit-one ::
 
   If active, quit help or edit mode, else exit the active transient.
 
   This is used when the user pressed {{{kbd(C-g)}}}.
 
 - Function: transient--do-quit-all ::
 
   Exit all transients without saving the transient stack.
 
   This is used when the user pressed {{{kbd(C-q)}}}.
 
 - Function: transient--do-suspend ::
 
   Suspend the active transient, saving the transient stack.
 
   This is used when the user pressed {{{kbd(C-z)}}}.
 
 * Classes and Methods
 #+cindex: 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.
 
 ** 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 (or “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.
 
 ** 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 {{{var(GROUP)}}} is non-~nil~, then
   it calls that function with {{{var(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.
 
 ** 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.
 
 ** 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 [[*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 [[*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 [[*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-variable~ class.
 
 - The ~transient-information~ class is special in that suffixes that use
   this class are not associated with a command and thus also not with
   any key binding.  Such suffixes are only used to display arbitrary
   information, and that anywhere a suffix can appear.  Display-only
   suffix specifications take this form:
 
   #+begin_src emacs-lisp
     ([LEVEL] :info DESCRIPTION [KEYWORD VALUE]...)
   #+end_src
 
   The ~:info~ keyword argument replaces the ~:description~ keyword used for
   other suffix classes.  Other keyword arguments that you might want to
   set, include ~:face~, predicate keywords (such as ~:if~), and ~:format~.
   By default the value of ~:format~ includes ~%k~, which for this class is
   replaced with the empty string or spaces, if keys are being padded in
   the containing group.
 
 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.
 
 ** Suffix Methods
 
 To get information about the methods implementing these generic
 functions use ~describe-function~.
 
 *** Suffix Value Methods
 
 - Function: transient-init-value obj ::
 
   This generic function sets the initial value of the object {{{var(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
   {{{var(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 {{{var(OBJ)}}}'s value.
 
 - Function: transient-infix-set obj value ::
 
   This generic function sets the value of infix object {{{var(OBJ)}}} to {{{var(VALUE)}}}.
 
 - Function: transient-infix-value obj ::
 
   This generic function returns the value of the suffix object {{{var(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 {{{var(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.
 
 *** Suffix Format Methods
 
 - Function: transient-format obj ::
 
   This generic function formats and returns {{{var(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 {{{var(OBJ)}}}'s ~key~ for display and returns the
   result.
 
 - Function: transient-format-description obj ::
 
   This generic function formats {{{var(OBJ)}}}'s ~description~ for display and
   returns the result.
 
 - Function: transient-format-value obj ::
 
   This generic function formats {{{var(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
   {{{var(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
   documentation string.
 
   For suffixes, show the command's documentation string.
 
   For infixes, show the manpage if that is specified.  Otherwise show
   the command's documentation string.
 
 ** Prefix Slots
 
 - ~show-help~, ~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 arbitrary non-suffix
   command is invoked.  See [[*Transient State]].
 
 - ~refresh-suffixes~ Normally suffix objects and keymaps are only setup
   once, when the prefix is invoked.  Setting this to ~t~, causes them to
   be recreated after every command.  This is useful when using ~:if...~
   predicates, and those need to be rerun for some reason.  Doing this
   is somewhat costly, and there is a risk of losing state, so this is
   disabled by default and still considered experimental.
 
 - ~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.  Arguments must me given in the same form as
   used in the ~argument~ or ~argument-format~ slot of the respective
   suffix objects, usually something like ~--switch~ or ~--option=%s~.  For
   options and ~transient-switches~ suffixes it is also possible to match
   against a specific value, as returned by ~transient-infix-value~,
   for example, ~--option=one~.
 
 - ~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
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 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 [[*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.
 
 ** 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 [[*Predicate Slots]].
 
 Also see [[*Suffix Classes]].
 
 *** Slots of ~transient-suffix~
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 - ~key~ The key, a key vector or a key description string.
 
 - ~command~ The command, a symbol.
 
 - ~transient~ Whether to stay transient.  See [[*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, which is
   called with zero or one argument (the suffix object), and returns a
   string.
 
 - ~face~ Face used for the description.  In simple cases it is easier
   to use this instead of using a function as ~description~ and adding
   the styling there.  ~face~ is appended using ~add-face-text-property~.
 
 - ~show-help~ A function used to display help for the suffix.  If
   unspecified, the prefix controls how help is displayed for its
   suffixes.
 
 *** Slots of ~transient-infix~
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 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 responsible 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 this is non-~nil~, then the values are read using
   ~completing-read-multiple~ by default and if you specify your own
   reader, then it should read the values using that function or
   similar.
 
   Supported non-~nil~ values are:
 
   - Use ~rest~ for an option that can have multiple values.  This is
     useful e.g., for an ~--~ argument that indicates that all remaining
     arguments are files (such as ~git log -- file1 file2~).
 
     In the list returned by ~transient-args~ such an option and its
     values are represented by a single list of the form ~(ARGUMENT
     . VALUES)~.
 
   - Use ~repeat~ for an option that can be specified multiple times.
 
     In the list returned by ~transient-args~ each instance of the option
     and its value appears separately in the usual from, for example:
     ~("--another-argument" "--option=first" "--option=second")~.
 
   In both cases the option's values have to be specified in the
   default value of a prefix using the same format as returned by
   ~transient-args~, e.g., ~("--other" "--o=1" "--o=2" ("--" "f1" "f2"))~.
 
 - ~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, {{{var(PROMPT)}}},
   {{{var(INITIAL-INPUT)}}} and {{{var(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, or a function that returns such a
   list.  The latter is not implemented for ~transient-switches~, because
   I couldn't think of a use-case.  How exactly the choices are used
   varies depending on the class of the suffix.
 
 *** Slots of ~transient-variable~
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 - ~variable~ The variable.
 
 *** Slots of ~transient-switches~
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 - ~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\\)~.
 
 ** 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.
 
 By default these predicates run when the prefix command is invoked,
 but this can be changes, using the ~refresh-suffixes~ prefix slot.
 See [[*Prefix Slots]].
 
 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 [[*Enabling and Disabling Suffixes]].
 
 * FAQ
 :PROPERTIES:
 :APPENDIX:   t
 :END:
 
 ** Can I control how the popup buffer is displayed?
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 Yes, see ~transient-display-buffer-action~ in [[*Configuration]].
 
 ** How can I copy text from the popup buffer?
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 To be able to mark text in Transient's popup buffer using the mouse,
 you have to add the below binding.  Note that for technical reasons,
 the region won't be visualized, while doing so.  After you have quit
 the transient popup, you will be able to yank it in another buffer.
 
 #+begin_src emacs-lisp
   (keymap-set transient-predicate-map
               "<mouse-set-region>"
               #'transient--do-stay)
 #+end_src
 
 ** How does Transient compare to prefix keys and universal arguments?
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 See https://github.com/magit/transient/wiki/Comparison-with-prefix-keys-and-universal-arguments.
 
 ** How does Transient compare to Magit-Popup and Hydra?
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 See https://github.com/magit/transient/wiki/Comparison-with-other-packages.
 
 ** Why did some of the key bindings change?
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 You may have noticed that the bindings for some of the common commands
 do *not* have the prefix {{{kbd(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., {{{kbd(M-p M-p M-p)}}} is much more convenient than {{{kbd(C-x M-p C-x M-p C-x M-p)}}}.
 
 You may also have noticed that the “Set” command is bound to {{{kbd(C-x s)}}},
 while Magit-Popup used to bind {{{kbd(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 {{{kbd(C-c)}}} all the bindings that begin with the {{{kbd(C-x)}}} prefix
 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.  {{{kbd(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.)
 
 ** Why does {{{kbd(q)}}} not quit popups anymore?
 :PROPERTIES:
 :UNNUMBERED: notoc
 :END:
 
 I agree that {{{kbd(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 {{{kbd(q)}}} to the
 command that turns ~magit-blame-mode~ off.
 
 So I had to decide if {{{kbd(q)}}} should quit the active transient (like
 Magit-Popup used to) or whether {{{kbd(C-g)}}} should do that instead, so that {{{kbd(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 {{{kbd(q)}}}.
 
 If you want to get {{{kbd(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 documentation string for more information.
 
 * Keystroke Index
 :PROPERTIES:
 :APPENDIX:   t
 :INDEX:      ky
 :COOKIE_DATA: recursive
 :END:
 * Command and Function Index
 :PROPERTIES:
 :APPENDIX:   t
 :INDEX:      fn
 :END:
 * Variable Index
 :PROPERTIES:
 :APPENDIX:   t
 :INDEX:      vr
 :END:
 * Concept Index
 :PROPERTIES:
 :APPENDIX:   t
 :INDEX:      cp
 :END:
 
 * GNU General Public License
 :PROPERTIES:
 :APPENDIX:   t
 :END:
 #+texinfo: @include gpl.texi
 
 * Copying
 :PROPERTIES:
 :COPYING:    t
 :END:
 
 #+begin_quote
 Copyright (C) 2018--{{{year}}} Free Software Foundation, Inc.
 
 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.
 #+end_quote
 
 #  LocalWords:  ARGLIST ARGS DOCSTRING ELEMENTs EVAL GROUPs Infixes
 #  LocalWords:  Infixes KEYWORDs LOC LocalWords MERCHANTABILITY Magit
 #  LocalWords:  Magit's Makefile OBJ OBJ's Pre arglist
 #  LocalWords:  args boolean booleans customizable docstring eval
 #  LocalWords:  featurep infixes init keymap keymaps loc magit manpage
 #  LocalWords:  minibuffer ness nilly noop plist pre prev
 #  LocalWords:  rebase src subclass subclasses subprocess superclass
 #  LocalWords:  utils
 
 # IMPORTANT: Also update ORG_ARGS and ORG_EVAL in the Makefile.
 # Local Variables:
 # indent-tabs-mode: nil
 # org-hide-macro-markers: t
 # org-src-preserve-indentation: nil
 # End: