In a regular expression, the question mark makes the preceding token optional.| 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
Explains the two regex flavors defined in the POSIX standard: Basic Regular Expressions and Extended Regular Expressions| www.regular-expressions.info
If you have written regular expressions before, you know that the regex syntax can be hard to keep track of. Certainly when writing a regex pattern that uses plenty of grouping and alternation.| www.regexbuddy.com