(flex.info)Comments in the Input

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5.4 Comments in the Input
=========================

Flex supports C-style comments, that is, anything between '/*' and '*/'
is considered a comment.  Whenever flex encounters a comment, it copies
the entire comment verbatim to the generated source code.  Comments may
appear just about anywhere, but with the following exceptions:

   * Comments may not appear in the Rules Section wherever flex is
     expecting a regular expression.  This means comments may not appear
     at the beginning of a line, or immediately following a list of
     scanner states.
   * Comments may not appear on an '%option' line in the Definitions
     Section.

   If you want to follow a simple rule, then always begin a comment on a
new line, with one or more whitespace characters before the initial
'/*').  This rule will work anywhere in the input file.

   All the comments in the following example are valid:

     %{
     /* code block */
     %}
     
     /* Definitions Section */
     %x STATE_X
     
     %%
         /* Rules Section */
     ruleA   /* after regex */ { /* code block */ } /* after code block */
             /* Rules Section (indented) */
     <STATE_X>{
     ruleC   ECHO;
     ruleD   ECHO;
     %{
     /* code block */
     %}
     }
     %%
     /* User Code Section */