## Backreferencing Backreferencing is used to match same text again. Backreferences match the same text as previously matched by a capturing group. Let's look at an example:

**Note:** `\/` is escaped `/`character, check it out in the appendix. The first captured group is (`\w+`), now we can use this group again by using a backreference (`\1`) at the closing tag, which matches the same text as in captured group `\w+`. You can backreference any captured group by using `\group_no`. Let's have two more examples:

### Backreferencing and character class Backreferencing can not be used in character class. Let's see an example:

### Backreferencing and quantifiers When we are using a backreference for an expression with quantifiers, then we have to be careful. Let's observe it:

Note that `(\d)+` and `(\d+)` both are different. So, what will happen for `(\d)+ -- \1` expression and same text above?

Can you observe something? For `(\d)+ -- \1` expression and `123 -- 3` string, first time 1 was stored in \1, then 2 was stored in \1 and at last 3 was stored. So, it will show a match if and only if the last character before ` --` is exactly same as the character after `-- `. **Problems:** 1. Match any palindrome string of length 6, having only lowercase letters. Answer: `([a-z])([a-z])([a-z])\3\2\1`

2. **RegEx**: `(\w+)oo\1le`
**Text:** `google, doodle jump, ggooggle, ssoosle` Answer:

**Note:** For group numbers more than 9, there is a syntax difference.