PREG_UNMATCHED_AS_NULL

PREG_UNMATCHED_AS_NULL is one of the accepted parameters for:

• preg_match parameter #4 (optionally as a bitmask)
• preg_match_all parameter #4 (optionally as a bitmask)

PREG constant: PREG_UNMATCHED_AS_NULL — This flag tells preg_match and preg_match_all to include unmatched subpatterns in $matches as null values. Without this flag, unmatched subpatterns are reported as empty strings, as if they were empty matches. Setting this flag allows to distinguish between these two cases. With preg_match, trailing unmatched subpatterns are omitted from $matches entirely unless this flag is used; as of PHP 7.4.0 the flag reports them as null, so that $matches always has the same size.

PREG_UNMATCHED_AS_NULL = 512;