(?is)applies the following effective flags to the remainder of the pattern: gis i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters
s modifier: single line. Allows a dot to match line terminators
<a the literal text <a (case insensitive) .*?any character, repeated any number of times
</a>the literal text </a> (case insensitive) (*SKIP)acts like (*PRUNE), but the next unanchored match attempt starts where (*SKIP) was reached instead of at the next subject character
(*F)forces the current match attempt to fail at this position