<!--the literal text <!-- \s*any whitespace character, repeated any number of times
\S+any non-whitespace character, repeated at least once
\s*any whitespace character, repeated any number of times
Non-Capturing Group(?:\n|.)* *repeats the group contents below any number of times:
\na line-feed (newline) character (ASCII 10)
.any character (except for line terminators)
<!--the literal text <!-- \s*any whitespace character, repeated any number of times
\1the text saved by group 1
\s*any whitespace character, repeated any number of times
g modifier: global. Finds all matches instead of stopping after the first