The configuration object with the following structure:
facetId - {string} - A friendly id for the facet.
Should be unique in the set of facets, and should be usable as a SPARQL variable.
predicate - {string} - The predicate or property path that defines the facet values.
hierarchy - {string} - The predicate or property path that defines the hierarchy of values.
classes - {Array} - The top level resources (URIs) of the hierarchy.
name - {string} - The title of the facet. Will be displayed to end users.
[enabled]{boolean} - Whether or not the facet is enabled by default.
If undefined, the facet will be disabled by default.
[endpointUrl]{string} - The URL of the SPARQL endpoint.
Optional, as it can also be given globally in
FacetHandler config.
[preferredLang] - {string|Array} - The language tag that is preferred
when getting labels for facet values, in case the value is a resource.
The default is 'en'.
Can also be a list of languages, in which case the languages are tried
in order.
If a label is not found in the given languages, a label without a
language tag is used. If a label is still not found,
the end part of the resource URI is used.
Supported label properties are skos:prefLabel, and rdfs:label.
[priority] - {number} - Priority for constraint sorting.
Undefined by default.