^start of line
httpsthe literal text https (case sensitive) .*any character (except for line terminators), repeated any number of times
index_the literal text index_ (case sensitive) \d+a digit, repeated at least once
.*any character (except for line terminators), repeated any number of times
\Zend of string, or before its final line terminator
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