Free-spacing is an alternative mode of the regular expression syntax. It can be turned on by using the
(?x) mode modifier.
When free-spacing mode is on, the whitespace (spaces, tabs, linefeeds) between regular expression tokens is ignored.
Note: In general, character classes, lookahead, lookbehind, named groups, and grouping modifiers are considered single tokens. Therefore, whitespace within these constructs is not igored even in free-spacing mode.
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