\d Matches a digit character.
\D Matches a non-digit character.
\s Matches any white space including spaces, tabs, form-feed characters, and so on.
\S Matches any non-white space character.
\w Matches any word character including underscore. This expression is equivalent to[A-Za-z0-9_].
\W Matches any non-word character. This expression is equivalent to[^A-Za-z0-9_].
Meta characters in regular expressions より引用
まず，\d は digit の頭文字， \s は space の頭文字， \w は word の頭文字です．
これらは小文字ですが，否定する場合は大文字にします．
