It's probably best left optional since the entire idea of having non-breaking spaces, is, not surprisingly, to prevent the breakage of something. Although admittedly overused on the Web at large, the principle is to provide a visual space between two 'words' which aren't meant to be separated. As such, something like 'Perl Monks' should not be treated as two words, but rather, as a single word. Including 0xA0 in \s would defeat the entire purpose of having   in the first place.

Instead, you could build methods into HTML::Message to strip out these invisible buggers, which is really only a single tr/\xA0/\x20/ operation anyway.

You might find that 0xA0 isn't the only "invisible" character out there either, as it depends on the font that you are using, and will likely vary from UNIX to Windows to Macintosh. Sometimes if the font doesn't have a defined character for that position, it draws nothing, a zero width non-character that is there, but not.