comment-use-syntax

comment-use-syntax is a variable defined in `newcomment.el'.
Its value is

undecided

Documentation:
Non-nil if syntax-tables can be used instead of regexps.
Can also be `undecided' which means that a somewhat expensive test will
be used to try to determine whether syntax-tables should be trusted
to understand comments or not in the given buffer.
Major modes should set this variable.