SWI-Prolog -- prolog:comment

prolog:comment_hook(+Comments, +Pos, +Term)

This hook allows for processing comments encountered by the compiler. If this hook is defined, the compiler calls read_term/2 with the option comments(Comments). If the list of comments returned by read_term/2 is not empty it calls this comment hook with the following arguments.

Comments is the non-empty list of comments. Each comment is a pair Position-String, where String is a string object (see section 5.2) that contains the comment including delimiters. Consecutive line comments are returned as a single comment.
Pos is a stream-position term that describes the starting position of Term
Term is the term read.

This hook is exploited by the documentation system. See stream_position_data/3. See also read_term/3.