allout-use-mode-specific-leader is a variable defined in `allout.el'.
Its value is

  • This variable is safe as a file local variable if its value
    satisfies the predicate which is a byte-compiled expression.

When non-nil, use mode-specific topic-header prefixes.

Allout outline mode will use the mode-specific `allout-mode-leaders' or
comment-start string, if any, to lead the topic prefix string, so topic
headers look like comments in the programming language. It will also use
the comment-start string, with an '_' appended, for `allout-primary-bullet'.

String values are used as literals, not regular expressions, so
do not escape any regular-expression characters.

Value t means to first check for assoc value in `allout-mode-leaders'
alist, then use comment-start string, if any, then use default (`.').
(See note about use of comment-start strings, below.)

Set to the symbol for either of `allout-mode-leaders' or
`comment-start' to use only one of them, respectively.

Value nil means to always use the default (`.') and leave
`allout-primary-bullet' unaltered.

comment-start strings that do not end in spaces are tripled in
the header-prefix, and an `_' underscore is tacked on the end, to
distinguish them from regular comment strings. comment-start
strings that do end in spaces are not tripled, but an underscore
is substituted for the space. [This presumes that the space is
for appearance, not comment syntax. You can use
`allout-mode-leaders' to override this behavior, when

You can customize this variable.