Simple filters that fail miserably

• Imagine I hate the <em> tag and only want to see <i> tags

• The filtering routine is easy to write:

      s!<(/?)em\b!<$1i!g;

• And so is the filter:

      $filter = HTTP::Proxy::BodyFilter::simple->new(
          sub { ${ $_[1] } =~ s!<(/?)em\b!<$1i!g; }
      );

• Except that the filter might (and surely will) receive a chunk of data containing an incomplete tag, like

      ove <b>&lt;em&gt;</b> tags, love, <em>love</e

• In this case, your regular expression won't match the closing tag and the transmogrified HTML will not be well-formed any more.

• You have to make sure no tag is cut. Maybe you could use HTML::Parser?