... unknown) Pattern Modifiers -- Describes possible modifiers in regex patterns . ... If this modifier is set, letters in the pattern match both upper and lower case letters. m (PCRE_MULTILINE) . By default, PCRE treats the subject string as consisting of a single "line" of characters (even if it actually contains several newlines). ... If there are no "\n" characters in a subject string, or no occurrences of ^ or $ in a pattern, setting this modifier has no effect. s (PCRE_DOTALL) . ...