i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters
s modifier: single line. Allows a dot to match line terminators
g modifier: global. Finds all matches instead of stopping after the first
m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string
U modifier: Ungreedy. Quantifiers are lazy by default. A trailing ? makes a quantifier greedy