The WhiteList MetadataFilter, identified by
type="Whitelist", deletes metadata for any entity not matched inside the plugin's configuration.
One attribute may be specified:
matcher specifies an EntityMatcher plugin to use to identify the entities to whitelist, allowing more flexible matching. Additional content will be included based on the type of plugin (see associated documentation).
Zero or more
<Include> elements may be specified. Each element's context is matched against each
entityID found in the source metadata to identify entities to keep.