The metacharacter "[" signals that the characters following,
up to the next "]", form a character class, that is, a regular expression
that matches any single character from the bracketed list. The character
class "[aA]" matches "a" or "A". A dash "-" is used to signify a range
of characters in the ASCII collating sequence. For example, "[a-zA-Z]"
matches any alphabetic character, while "[0-9]" matches any numeric
character. If the first character in a character class is an "^",
then any character not in the class constitutes a match; for example,
[^a] matches any character except an "a".
Metacharacters
Expression Closure (Match Zero or More of the Previous Expressions)
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