Regex Notes

Content

(?s) For “single line mode” makes the dot match all characters, including line breaks. Not supported by Ruby or JavaScript.
*? Ungreedy
(?<=(regex)) Positive Lookbehind
(?<!(regex)) Negative Lookbehind
(?=(regex)) Positive Lookahead
(?!(regex)) Negative Lookahead

Reference:

Regular-Expressions.info Tutorial