The FilterName, e.g. "Ort" or "Energieträger" (see filterColumns()).
The operator.
OptionalvalueThe value, quoted by buildFilter. For a dropdown column pass its code; an array
becomes the comma list the register reads as "any of these codes". Ignored for
null/nn (sent as ''). Must not contain ~ (nor , in an array item).
One condition for buildFilter.