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Is the entire string


matched by the regular expression


No. ([XY]++) matches YYXX and keeps possession that substring. So group 1 is YYXX and so \1 does not match the XX at the end of the string.

List of Possessive Quantifiers

Any of the quantifiers can be made possessive

Possessive Quantifiers
matches as many of X
as it can and keeps hold of them
X?+ zero or one X
X*+ zero or more X
X++ one or more X
X{n}+ exactly n X
X{n,}+ n or more X
X{n,m}+ n up to m X

For example, X{2,5}+ will match between two and five X, and keeps what it has matched.

The expression X{2}+ must match exactly two X and is equivalent to X{2}? and is equivalent to X{2}.


Which of the following regular expressions match the complete string abc123defg ?