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PHP Manual

# Predefined Constants

The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.

PREG constants
constant | description | since
--- | --- | ---
`PREG_PATTERN_ORDER` | Orders results so that $matches[0] is an array of full pattern matches, $matches[1] is an array of strings matched by the first parenthesized subpattern, and so on. This flag is only used with preg_match_all. |
`PREG_SET_ORDER` | Orders results so that $matches[0] is an array of first set of matches, $matches[1] is an array of second set of matches, and so on. This flag is only used with preg_match_all. |
`PREG_OFFSET_CAPTURE` | See the description of `PREG_SPLIT_OFFSET_CAPTURE`. | 4.3.0
`PREG_SPLIT_NO_EMPTY` | This flag tells preg_split to return only non-empty pieces. |
`PREG_SPLIT_DELIM_CAPTURE` | This flag tells preg_split to capture parenthesized expression in the delimiter pattern as well. | 4.0.5
`PREG_SPLIT_OFFSET_CAPTURE` | If this flag is set, for every occurring match the appendant string offset will also be returned. Note that this changes the return values in an array where every element is an array consisting of the matched string at offset 0 and its string offset within subject at offset 1. This flag is only used for preg_split. | 4.3.0
`PREG_NO_ERROR` | Returned by preg_last_error if there were no errors. | 5.2.0
`PREG_INTERNAL_ERROR` | Returned by preg_last_error if there was an internal PCRE error. | 5.2.0
`PREG_BACKTRACK_LIMIT_ERROR` | Returned by preg_last_error if backtrack limit was exhausted. | 5.2.0
`PREG_RECURSION_LIMIT_ERROR` | Returned by preg_last_error if recursion limit was exhausted. | 5.2.0
`PREG_BAD_UTF8_ERROR` | Returned by preg_last_error if the last error was caused by malformed UTF-8 data (only when running a regex in UTF-8 mode). | 5.2.0
`PREG_BAD_UTF8_OFFSET_ERROR` | Returned by preg_last_error if the offset didn't correspond to the begin of a valid UTF-8 code point (only when running a regex in UTF-8 mode). | 5.3.0
`PCRE_VERSION` | PCRE version and release date (e.g. "7.0 18-Dec-2006"). | 5.2.4