Re: comma in macro body produces `` in tex output

[Karl Berry]

    @macro explain{line}
    \line\
    @end macro
    @explain{a\,b}

The manual explains (in the Invoking Macros node):

      To insert a comma, brace, or backslash in an argument, prepend a
    backslash, as in

         @MACNAME {\\\{\}\,}

    which will pass the (almost certainly error-producing) argument `\{},'
    to MACNAME.

Hope that works ...