?repeats the group contents below at most once:
\sa Unicode whitespace character
keythe literal text key (case sensitive) \sa Unicode whitespace character
0-9one character from 0 (4810) to 9 (5710)
\sa Unicode whitespace character
\Sany character that is not Unicode whitespace
Character Class[a-zA-Z0-9]+ +matches at least one character from the set below:
a-zone character from a (9710) to z (12210) (case sensitive)
A-Zone character from A (6510) to Z (9010) (case sensitive)
0-9one character from 0 (4810) to 9 (5710)
\Sany character that is not Unicode whitespace