[%# Note that error messages should generally be indented four spaces, like
  # below, because when Bugzilla translates an error message into plain
  # text, it takes four spaces off the beginning of the lines. 
  #
  # Note also that I prefixed my error name with "example", the name of my
  # extension, so that I wouldn't conflict with other error names in
  # Bugzilla or other extensions.
  #%]
[% IF error == "example_my_error" %]
   [% title = "Example Error Title" %]
   This is the error message! It contains <em>some html</em>.
[% END %]