<value>) pair is already in the input.
+
With `add`, a new trailer will be added, even if some trailers with
the same (<key>, <value>) pair are already in the input.
+
With `replace`, an existing trailer with the same <key> will be
deleted and the new trailer will be added. The deleted trailer will be
the closest one (with the same <key>) to the place where the new one
will be added.
+
With `doNothing`, nothing will be done; that is no new trailer will be
added if there is already one with the same <key> in the input.

trailer.ifmissing::
	This option makes it possible to choose what action will be
	performed when there is not yet any trailer with the same
	<key> in the input.
+
The valid values for this option are: `add` (this is the default) and
`doNothing`.
+
With `add`, a new trailer will be added.
+
With `doNothing`, nothing will be done.

trailer.<keyAlias>.key::
	Defines a <keyAlias> for the <key>. The <keyAlias> must be a
	prefix (case does not matter) of the <key>. For example, in `git
	config trailer.ack.key "Acked-by"` the "Acked-by" is the <key> and
	the "ack" is the <keyAlias>. This configuration allows the shorter
	`--trailer "ack:..."` invocation on the command line using the "ack"
	<keyAlias> instead of the longer `--trailer "Acked-by:..."`.
+
At the end of the <key>, a separator can appear and then some
space characters. By default the only valid separator is ':',
but this can be changed using the `trailer.separators` config
variable.
+
If there is a separator in the key, then it overrides the default
separator when adding the trailer.

trailer.<keyAlias>.where::
	This option takes the same values as the 'trailer.where'
	configuration variable and it overrides what is specified by
	that option for trailers with the specified <keyAlias>.

trailer.<keyAlias>.ifexists::
	This option takes the same values as the 'trailer.ifexists'
	configuration variable and it overrides what is specified by
	that option for trailers with the specified <keyAlias>.

trailer.<keyAlias>.ifmissing::
	This option takes the same values as the 'trailer.ifmissing'
	configuration variable and it overrides what is specified by
	that option for trailers with the specified <keyAlias>.

trailer.<keyAlias>.command::
	Deprecated in favor of 'trailer.<keyAlias>.cmd'.
	This option behaves in the same way as 'trailer.<keyAlias>.cmd', except
	that it doesn't pass anything as argument to the specified command.
	Instead the first occurrence of substring $ARG is replaced by the
	<value> that would be passed as argument.
+
Note that $ARG in the user's command is
only replaced once and that the original way of replacing $ARG is not safe.
+
When both 'trailer.<keyAlias>.cmd' and 'trailer.<keyAlias>.command' are given
for the same <keyAlias>, 'trailer.<keyAlias>.cmd' is used and
'trailer.<keyAlias>.command' is ignored.

trailer.<keyAlias>.cmd::
	This option can be used to specify a shell command that will be called
	once to automatically add a trailer with the specified <keyAlias>, and then
	called each time a '--trailer <keyAlias>=<value>' argument is specified to
	modify the <value> of the trailer that this option would produce.
+
When the specified command is first called to add a trailer
with the specified <keyAlias>, the behavior is as if a special
'--trailer <keyAlias>=<value>' argument was added at the beginning
of the "git interpret-trailers" command, where <value>
is taken to be the standard output of the command with any
leading and trailing whitespace trimmed off.
+
If some '--trailer <keyAlias>=<value>' arguments are also passed
on the command line, the command is called again once for each
of these arguments with the same <keyAlias>. And the <value> part
of these arguments, if any, will be passed to the command as its
first argument. This way the command can produce a <value> computed
from the <value> passed in the '--trailer <keyAlias>=<value>' argument.