Function func

func(name, ...args): OGCCondition
Creates a custom OGC function with the given name and arguments.
```
  FilterFactory.func(
    "getCityName"
  );
```
```
  FilterFactory.func(
    "geometryType",
    FilterFactory.property( "geom" )
  );
```
Parameters
- name: string
  The name of a custom function
- Rest...args: Expression[]
  The arguments that should be passed to the function. This can be any number of OGCExpression.
Returns OGCCondition
The custom OGC function