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Internal option settingThe settings of PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, PCRE_UNGREEDY, PCRE_EXTRA, PCRE_EXTENDED and PCRE_DUPNAMES can be changed from within the pattern by a sequence of Perl option letters enclosed between "(?" and ")". The option letters are:
For example, (?im) sets case-insensitive (caseless), multiline matching. It is also possible to unset these options by preceding the letter with a hyphen, and a combined setting and unsetting such as (?im-sx), which sets PCRE_CASELESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED, is also permitted. If a letter appears both before and after the hyphen, the option is unset.
When an option change occurs at top level (that is, not inside
subpattern parentheses), the change applies to the remainder of the
pattern that follows. So
If an option change occurs inside a subpattern, the effect
is different. This is a change of behaviour in Perl 5.005.
An option change inside a subpattern affects only that part
of the subpattern that follows it, so
The PCRE-specific options PCRE_UNGREEDY and PCRE_EXTRA can be changed in the same way as the Perl-compatible options by using the characters U and X respectively. The (?X) flag setting is special in that it must always occur earlier in the pattern than any of the additional features it turns on, even when it is at top level. It is best put at the start. |