comment [<anything>]

The comment command does nothing. It is important to understand that the comment command is a proper command, and follows the rules for ircII syntax. You can create a multi-line comment by surrounding it in curly braces

 comment {
    This is a multi line comment
    Isn't that neat?
 }

The comment command is also known as : (colon). Remember that in ircII, command names are not limited, so yes, the colon is itself a proper command, and is the comment command

  : {
      This is another multi-line comment
      This is so much less hacky than the old C-style comments!
  }

It is helpful to contrast the comment command (which is a proper ircII command) from the #-comment. The #-comment is a load time thing. #-comments are discarded by load and do not become part of the script when it is run. #-comments do not support multi-line comments (as above), and they end at the end of the line. For this reason, #-comments are better for commenting out real code

The comment command is retained by load because it is a full blown command and is part of the ircII syntax. This means that comment commands are parsed each time they are encountered, which means you don't want to use them inside of aliases (they would slow the alias name).

The standard loader supports C /* */ multi-line comments, but that is for backwards compatability. They should not be used in new code. Use the examples above instead.