⭐ in reply to What can regular expressions NOT do?
Regexps are bad at very complicated cases, especially when
things are nested. The typical example is HTML: it's easy enough
to make a simple regexp to grab tags, but to get it really right
and account for all cases (comments, greater than signs within quotes
within HTML tags, multiline tags, etc.) you outgrow the usefullness
of a regular expression and really need something that will
actually parse the string (or file, whatever) that contains
the HTML. Luckily, there are modules that will do just that
for you.
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Seekers of Perl Wisdom