In a regular expression, square brackets are used to indicate character classes, which matches any of the characters in the character set.| www.regular-expressions.info
In a regular expression, the asterisk or star causes the preceding token to be matched zero or more times, and the plus one or more times.| www.regular-expressions.info
In a regular expression, the vertical bar or pipe symbol tells the regex engine to match any of two or more options| www.regular-expressions.info
In a regular expression, parentheses can be used to group regex tokens together and for creating backreferences. Backreferences allow you to reuse part of the regex match in the regex, or in the replacement text.| www.regular-expressions.info
Learn how to use regular expressions with Tcl’s regexp and regsub commands| www.regular-expressions.info
In a regular expression, POSIX bracket expressions can be used to match one of a certain kind of characters.| www.regular-expressions.info