Flags or Modifiers

g

Global match

i

Ignore case

m

Multiple lines (^ and $ match start and end of a line)

s

Single line (. matches newline)

x

Specifies that whitespace characters in the pattern are ignored except when escaped or inside a character class

J

Duplicate group names allowed

U

Ungreedy quantifiers

A

Anchored, the pattern is forced to match only at the beginning (^)

E

Anchored, the pattern is forced to match only at the end ($)