...
my $tagname;
sub start {
        my ($self, $tag, $attr, $attrseq, $origtext) = @_;
        $tagname = $tag;  # store tag name for later use

        if ($tag =~ /^span$/i && $attr->{'class'} =~ /^main-content$/i)
        {
            # set if we find <span class="main-content"
            $content_flag = 1;
        }
  }
sub text {
        my ($self, $text) = @_;
        # If we're in <H1>...</H1> or
        my $tagged_text = $text !~ /^\s*$/ ? "<$tagname>$text</$tagname>" : $text;
        if ($content_flag)    { $main_content    .= $tagged_text; }
}
...