# Capture an entire line that contains a word
(?=.*WORD).*
# Capture an entire line that contains two words in any order
(?=.*WORD1)(?=.*WORD2).*
# Capture entire lines that contain either WORD[1-3] from left to right
(?=.*WORD1|WORD2|WORD3).*
Capture entire lines that contain WORD[1-3] from left to right
(.*?=WORD1|WORD2|WORD3).*
# Capture every word in the string EXCEPT the words in the list
(?>[\w-]+)(?<!WORD1|WORD2|WORD3|WORD4)
# Capture every part of the string that comes before WORD
.*(?=WORD)
# Capture every part of the string that comes after WORD
(?<=WORD).*
# Capture every part of the string that comes between two words
(?<=WORD1).*(?=WORD2)
# Captures the first word after WORD
(?<=WORD)\s+(\w+)
# Captures the words on either side (left and right) of the word WORD
\w+(?=\sWORD)|(?<=WORD\s)\w+
# Capture a phrase if it exists in the string and return that phrase
\b(To Be Or Not To Be)\b
# Capture a phrase if it exists in a string (this one does not use word boundaries so it must account for blank spaces)
(To\sBe\sOr\sNot\sTo\sBe)
# Capture any word that appears twice in a string
(\b\w+\b)(?=[\s\S]*\b\1\b)
# Capture any phrase that appears twice in a string
(\b\w+\s+\S+\b)(?=[\s\S]*\b\1\b)
