The following are regular expression examples which will match:

• An entire line.
  ^.*$
• Blank lines.
  ^$
• Whitespace on a line.
  \s+
• Whitespace across lines.
  (?n\s+)
• Whitespace that spans at least two lines. Note minimal matching *? quantifier.
  (?n\s*?\n\s*)
• IP address (not robust).
  (?:\d{1,3}(?:\.\d{1,3}){3})
• Two character US Postal state abbreviations (includes territories).
  [ACDF-IK-PR-W][A-Z]
• Web addresses.
  (?:https?://)?www\.\S+
• Case insensitive double words across line breaks.
  (?i(?n<(\S+)\s+\1>))
• Upper case words with possible punctuation.
  <[A-Z][^a-z\s]*>