Merge pull request #1224 from izzergh/feature/update-regexp

Add Lookahead and Lookbehind to regexp.md

regexp.md

@@ -5,6 +5,7 @@ layout: 2017/sheet
 weight: -1
 authors:
   - github: rizqyhi
+  - github: izzergh
   - github: kolapsys
   - github: samtrion
 updated: 2019-11-14
@@ -76,3 +77,12 @@ description: |
 | `a{3,}`  | Match 3 or more       |
 | `a{1,3}` | Match between 1 and 3 |
 
+### Lookahead & Lookbehind
+
+| Pattern      | Description                               |
+| ---          | ---                                       |
+| `a(?=b)`     | Match `a` in `baby` but not in `bay`      |
+| `a(?!b)`     | Match `a` in `Stan` but not in `Stab`     |
+| ---          | ---                                       |
+| `(?<=a)b`    | Match `b` in `crabs` but not in `cribs`   |
+| `(?<!a)b`    | Match `b` in `fib` but not in `fab`       |