Je was op zoek naar: parenthesized (Engels - Koreaans)

a description of how this works is given later, following the discussion of parenthesized subpatterns.
although lookbehind assertions must match fixed length strings, each alternative branch of a lookbehind assertion can match a different length of string. perl 5.005 requires them all to have the same length.

if this flag is set, parenthesized expression in the delimiter pattern will be captured and returned as well.
flags can be any combination of the following flags (combined with bitwise _bar_ operator):

this flag tells preg_split() to capture parenthesized expression in the delimiter pattern as well.
/^(?i)php[34]/

if pattern contains parenthesized substrings, replacement may contain substrings of the form\\ digit, which will be replaced by the text matching the digit' th parenthesized substring; \\0 will produce the entire contents of string.
(php 3, php 4)