pegjs/docs/grammar/backtracking.md
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### Backtracking
Unlike in regular expressions, there is no backtracking in PEG.js expressions.
For example, using the input "hi!":
```pegjs
// This will fail
HI = "hi" / "hi!"
// This will pass
HI = "hi!" / "hi"
// This will also pass
HI = w:"hi" !"!" { return w } / "hi!"
```
For more information on backtracking in PEG.js, [checkout this excellent answer on Stack Overflow](https://stackoverflow.com/a/24809596/1518408).