Here's an efficient way to properly match HTML comments in a string of text. I use the "unrolling the loop" technique, and thus the commenting ability is helpful.

$COMMENT_rex = qr{
  <!--            # opening <!--
  [^-]*           # 0 or more non hyphens
  (?:
    (?! -- \s* > )  # as long as it's NOT a -->
    -               # -
    (?:
      -             # -
      [^-]*         # 0 or more non -
      (?: - [^-]+ )*  # -, 1 or more non -, 0 or more times
    )?              # optionally...
    [^-]*           # 0 or more non -
  )*              # 0 or more times
  -- \s* >        # the ending -->
}x;
[download]

The regex itself is complex, because the element it's matching is complex. Here's the unadulterated regex:

$COMMENT_rex =
  qr{<!--[^-]*(?:(?!--\s*>)-(?:-[^-]*(?:-[^-]+)*)?[^-]*)*--\s*>};
[download]

Ick.

japhy -- Perl and Regex Hacker