Function optional

optional(regex: StdRegex): StdRegex
This is like the ? postfix operator.
Parameters
- regex: StdRegex
Returns StdRegex
Example
```
optional(singleChar('a')) // like /a?/
```
- Defined in regex.ts:331
optional(regex: ExtRegex): ExtRegex
This is like the ? postfix operator.
Parameters
- regex: ExtRegex
Returns ExtRegex
Example
```
optional(singleChar('a')) // like /a?/
```
- Defined in regex.ts:332