[Apache]RewriteRule regular expressions

Text:
. Any single character
[chars] Character class: One of chars
[^chars] Character class: None of chars
text1|text2 Alternative: text1 or text2

Quantifiers:
? 0 or 1 of the preceding text
* 0 or N of the preceding text (N > 0)
+ 1 or N of the preceding text (N > 1)

Grouping:
(text) Grouping of text
(either to set the borders of an alternative or
for making backreferences where the Nth group can
be used on the RHS of a RewriteRule with $N)

Anchors:
^ Start of line anchor
$ End of line anchor

Escaping:
\char escape that particular char
(for instance to specify the chars ".[]()" etc.)