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Adding note about regex performance #18

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Adding note about regex performance #18

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7 changes: 7 additions & 0 deletions s/regexes.md
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Expand Up @@ -52,3 +52,10 @@ employed by HTML. HTML is not a regular language and hence cannot be
parsed by regular expressions. Regex queries are not equipped to break
down HTML into its meaningful parts. HTML is a language of sufficient
complexity that it cannot be parsed by regular expressions.

In addition, the performance of regular expressions can be
unpredictable, and a few small tweaks to the expression may
unexpectedly result in much worse performance (depending on the
expression, the language, and engine). This is particularly true when
using features such as positive or negative lookahead or lookbehind,
which might be desireable for HTML parsing tasks.