## KorAP: Regular Expressions

Regular expressions are patterns describing a set of strings.

In the KorAP backend a wide range of operators is supported, but only the following are guaranteed to be stable throughout the system:

### Operators

`.`

- Any- Any symbol
`()`

- Group- Create a group of operands
`|`

- Alternation- Create alternative operands
`[]`

- Character Class- Group alternative characters
`\`

- Escape symbol- Mark the following character to be interpreted as verbatim, when the character is special (i.e. an operator or quantifier)

`".eine" Frau`

`"Fr..de"`

`"Fr(ie|eu)de" []{,3} Eierkuchen`

`"Fre[um]de"`

`"b.w\."`

### Quantifiers

Operands in regular expressions can be quantified, meaning they are allowed to occur consecutively a specified number of times. The following quantifieres are supported:

`?`

- Match 0 or 1 times
`*`

- Match 0 or more times
`+`

- Match 1 or more times
`{n}`

- Match
`n`

times `{n,}`

- Match at least
`n`

times `{n,m}`

- Match at least
`n`

times but no more than`m`

times

`"Schif+ahrt"`

`"kl?eine" Kinder`

`"Schlos{2,3}traße"`

`"Rha(bar){2}"`