```
| X, as a named-capturing group |
^ non-capturing ^^
| (?:X) | X, as a non-capturing group |
| (?>X) | X, as an independent, non-capturing group |
^ Assertion (See Regexp - Look-around group (Assertion) - ( Lookahead | Lookbehind )) ^^
| (?=X) | X, positive lookahead (via zero-width) |
| (?!X) | X, negative lookahead (via zero-width) |
| (?<=X) | X, positive lookbehind (via zero-width) |
| (?<!X) | X, negative lookbehind (via zero-width) |
^ Flag ^^
| (?idmsuxU-idmsuxU) | Nothing, but turns match flags i d m s u x U on - off |
| (?idmsux-idmsux:X) | X, as a non-capturing group with the given flags i d m s u x on - off |
===== Name =====
By default, the group is indexed by index (0,1,2,…) but you can give it a name with the following syntax
(?X)where X is the regular expression pattern that you want to captureIt's called a named-capturing group.IndexCapturing groups are numbered by counting their opening parentheses from left to right. In the expression ((A)(B(C))), for example, there are the following groups:
```
- 0 - Group zero always stands for the entire expression - ((A)(B(C)))
- 1 - ((A)(B(C)))
- 2 - (A)
- 3 - (B(C))
- 4 - (C)

Non-CapturingBasicA non capturing group will not be indexed.In the expression (?:A)(B)(C), for example, there are the following groups:
- 0 - Group zero always stands for the entire expression - (?:A)(B)(C)
- 1 - (B)
- 2 - (C)

The group (?:A) was not captured.Look-aroundRegexp - Look-around group (Assertion) - ( Lookahead | Lookbehind )SubstitutionWhen you want to use the content of each captured group, you will generally use the following substitution construct:
- n for the group index
- groupName for the group name

When using group index, this construct must be used when:
- the number of group is greater than 9
- you want a number that follow the substitution

The dollar is also not always mandatory:
- n for the group index
- groupName for the group name

Their is also a shorthand notation for groups up to 9.
Symbol Definition
\0 backreference to the entire expression
\1 backreference to group 1
\2 backreference to group 2
\n backreference to group n

ExampleThe below regular expression has two groups
`([^ ]) (.*)`

where:
- the first group is [^ ] which will parse all non space characters.
- the second group is .* which will take all characters.

if you parse the following text:
```
Hello World
```

You will get:
- in the first group, \1, the text Hello
- and in the second group, \2, the text World

See more example here: A step by step on how to replace a text in Notepad++ with regular expression

```
```