All Perl code within source HTML files has to be embedded into
standard HTML comment tags of one of the following forms:

<!-- perl -->
    This tag allows arbitrary perl code to be included between the
    opening '<!-- perl' and the closing '-->' tags. The current
    implementation uses a non-greedy pattern matching, so HTML
    comment tags inside the perl comment tags will produce unexpected
    results.

<!-- =perl $var -->
    This form allows the interpolation of a single variable between
    the opening '<!-- perl' and the closing '-->' tags.
    These tags don't break up a print statement.

<!-- =perl -->Placeholder text<!-- /perl --->
    As above, additionally "Placeholder text" and the closing tags
    are removed

<!-- perl dummy start --> <!-- perl dummy end -->
    These tags and all characters in between are weeded out.