m turns the match criteria into multiline, meaning that ^ $ will match the beginning/end of a line rather than the whole string (in other words, change “^” and “$” from matching the start or end of the string to matching the start or end of any line anywhere within the string)<br /> In multi-line mode $ also matches before every newline character.<br /> (…) in multi-line mode also matches after every newline character.

s which turns the code into a string which will allow you to match over many lines. In this case only, . matches also a newline, in all other cases, . matches any character except \n