More options are described in Common Suffix Commands, in Saving Values, in Using History and in Enabling and Disabling Suffixes.
Also see Common Suffix Commands.
This option controls whether the current transient’s infix and suffix commands are shown in the popup buffer.
t (the default) then the popup buffer is shown as soon as a
transient prefix command is invoked.
nil, then the popup buffer is not shown unless the user
explicitly requests it, by pressing an incomplete prefix key
sequence.
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).
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:
This option specifies the action used to display the transient popup
buffer. The transient popup buffer is displayed in a window using
(display-buffer BUFFER transient-display-buffer-action).
The value of this option has the form (FUNCTION . ALIST),
where FUNCTION is a function or a list of functions. Each such
function should accept two arguments: a buffer to display and an
alist of the same form as ALIST. See (elisp)Choosing Window,
for details.
The default is:
(display-buffer-in-side-window (side . bottom) (inhibit-same-window . t) (window-parameters (no-other-window . t)))
This displays the window at the bottom of the selected frame.
Another useful FUNCTION is display-buffer-below-selected, which
is what magit-popup used by default. For more alternatives see
(elisp)Buffer Display Action Functions, and see (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.
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.
This option controls whether the transient popup buffer has a mode-line, separator line, or neither.
If nil, then the buffer has no mode-line. If the buffer is not
displayed right above the echo area, then this probably is not a
good value.
If line (the default), then the buffer also has no mode-line, but a
thin line is drawn instead, using the background color of the face
transient-separator. Text-mode frames cannot display thin lines,
and therefore fall back to treating line like nil.
Otherwise this can be any mode-line format. See (elisp)Mode Line Format, for details.
This option controls whether prefixes and suffixes are colored in a Hydra-like fashion.
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.
For more information about how Hydra uses colors see https://github.com/abo-abo/hydra#color and https://oremacs.com/2015/02/19/hydra-colors-reloaded.
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.
This function is used to modify key bindings. If the value of this
option is nil (the default), then no substitution is performed.
This function is called with one argument, the prefix object, and
must return a key binding description, either the existing key
description it finds in the key slot, or the key description that
replaces the prefix key. It could be used to make other
substitutions, but that is discouraged.
For example, = is hard to reach using my custom keyboard layout, so I substitute ( for that, which is easy to reach using a layout optimized for lisp.
(setq transient-substitute-key-function
(lambda (obj)
(let ((key (oref obj key)))
(if (string-match "\\`\\(=\\)[a-zA-Z]" key)
(replace-match "(" t t key 1)
key))))
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.
This option controls whether the transient buffer is hidden while user input is being read in the minibuffer.
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.
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.
These options are mainly intended for developers.
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.
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.