<Buttonthe literal text <Button (case sensitive) .*any character (except for line terminators), repeated any number of times
classNamethe literal text className (case sensitive) .*any character (except for line terminators), repeated any number of times
>the literal > (6210 / 768 / 3E16)
m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string
g modifier: global. Finds all matches instead of stopping after the first