Similar to the LaTeX converter, you can use either tt(NOTRANS) or
tt(htmlcommand) to send HTML commands to the output. Or, since the only 
`difficult' characters are probably only tt(<) and tt(>), you can also resort 
to tt(CHAR) for these two characters.

Furthermore, the HTML converter defines the macro tt(htmltag), expecting two 
arguments: the tag to set, and an `on/off' switch. E.g., tt(htmltag(b)(1)) 
sets tt(<b>) while tt(htmltag(b)(0)) sets tt(</b>).

E.g., the following code sends a HTML command tt(<hr>) to the output file when 
in HTML mode:

verb(\
COMMENT(-- alternative 1, using htmlcommand --)
htmlcommand(<hr>)

COMMENT(-- alternative 2, using NOTRANS --)
IFDEF(html)\ 
    (NOTRANS(<hr>))\ 
    ()

COMMENT(-- alternative 3, using CHAR --)
IFDEF(html)\ 
    (CHAR(C)HAR(<)hr+CHAR(C)HAR(>))\ 
    ()
    
COMMENT(-- alternative 4, using htmltag --)
htmltag(hr)(1))
