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Can regex be used to check if input conforms to a very strict subset of HTML? The theoretical answer is Yes. The Javascript regex language is more than powerful enough to parse a recursive gramm...
Answer
#2: Post edited
by
Stephen C
·
2020-09-20T05:23:16Z (about 4 years ago)
- > Can regex be used to check if input conforms to a very strict subset of HTML?
The theoretical answer is Yes. The Javascript regex language is more powerful than enough to parse a recursive grammar.- In practice it is a bad idea.
- 1. Bugs! Writing a regex that can validate arbitrarily nested HTML elements (including the context rules) is complicated. _Thoroughly_ testing the regex is difficult.
- 2. Writing a recursive regex that is not vulnerable to a "backtracking attack" could be difficult. Such an attack would entail crafting some input HTML that would trigger [catastrophic backtracking](https://www.regular-expressions.info/catastrophic.html) ... in a regex that wasn't designed to defend against this problem.
- > Can regex be used to check if input conforms to a very strict subset of HTML?
- The theoretical answer is Yes. The Javascript regex language is more than powerful enough to parse a recursive grammar.
- In practice it is a bad idea.
- 1. Bugs! Writing a regex that can validate arbitrarily nested HTML elements (including the context rules) is complicated. _Thoroughly_ testing the regex is difficult.
- 2. Writing a recursive regex that is not vulnerable to a "backtracking attack" could be difficult. Such an attack would entail crafting some input HTML that would trigger [catastrophic backtracking](https://www.regular-expressions.info/catastrophic.html) ... in a regex that wasn't designed to defend against this problem.
#1: Initial revision
by
Stephen C
·
2020-09-17T01:37:34Z (over 4 years ago)
> Can regex be used to check if input conforms to a very strict subset of HTML? The theoretical answer is Yes. The Javascript regex language is more powerful than enough to parse a recursive grammar. In practice it is a bad idea. 1. Bugs! Writing a regex that can validate arbitrarily nested HTML elements (including the context rules) is complicated. _Thoroughly_ testing the regex is difficult. 2. Writing a recursive regex that is not vulnerable to a "backtracking attack" could be difficult. Such an attack would entail crafting some input HTML that would trigger [catastrophic backtracking](https://www.regular-expressions.info/catastrophic.html) ... in a regex that wasn't designed to defend against this problem.