Each category can define a list of filters. This is an additional JSON value with the key "filter", e.g.:
```json
{
"query": {
"13": "nwr[amenity]"
},
"filter": {
"type": {
"name": "{{ keyTrans('amenity') }}",
"type": "select",
"values": {
"bar": {
"nwr[
},
}
}
}
```
This defines a filter with the ID 'type' and the translated name of the key 'amenity'. It's of type 'select' and has several possible values.
Each filter can define the following values:
* name: Name of the filter. String, which can make use of twig functions, e.g. `keyTrans` as in the above example.
* type: A form type, e.g. 'text', 'select', 'radio', 'checkbox'
* values: Possible values. Can either be an array, an object or a html string with several `
{% endfor %}
```
* Name is generated from text content. If it is empty, it can be created via `valueName`.
* Query is optional, it can be created from key (or filter id), op and the value.