I was researching more on Regular Expressions and came across this
nice presentation: http://swtch.com/~rsc/regexp/regexp1.html , what
caught my attention was the title:

Regular Expression Matching Can Be Simple And Fast
(but is slow in Java, Perl, PHP, Python, Ruby, ...)

I thought I'll share the above presentation as regular expressions in
XPath are based on Perl.

Some companies go through millions of lines of data, in such cases I
guess there would be a need to optimize the speed. This is just a
thought.