Standard Meta Characters
Backreferences
\#, where # is an integer, is a backreference to the last substring matching the # parenthetical in the regular expression (counting left parentheses).
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in the string "Bart, Lisa, Maggie" the regular expression /Bart(,)Lisa\1/ matches "Bart, Lisa," |
Note that paired parentheses are numbered by counting left parentheses from the left.