lucy24 - 9:23 pm on Apr 27, 2013 (gmt 0)
If each file or directory name consists entirely of \w then constructing Regular Expressions is dead easy. Permit hyphens, and right away everything has to change from \w to [\w-]. Permit additional punctuation and soon you are into [^blahblah] territory instead.
Literal periods are particularly troublesome because they do have meaning as punctuation: separating the various components of the hostname at one end of the URL; separating filename from extension at the other end. So you're on a three-way toggle between "means A", "means B", and "means nothing".
Anyway, the Great Divide is that a lowline is \w while all other punctuation is \W