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module providing full support for regular expressions
to avoid confusion with regex, we use raw strings
a, X, 9
. (a period)
matches any single character except newline '\n'
matches a "word" character: a letter or digit or underbar [a-zA-Z0-9_]r
matches any non-word character.
boundary between word and non-word
matches a single whitespace character: space, newline, return, tab
matches any non-whitespace character
\t, \n, \r
tab, newline, return
decimal digit [0-9]
matches start of the string
match the end of the string
inhibit the "specialness" of a character