CWLHintsItem

A single entry of a process's hints list: any one of the requirement/hint classes this register models (the standard CWL requirements, plus the OGC-AP/WPS1/builtin hint classes), or UnknownRequirement as a fallback for any other class-discriminated hint not otherwise recognized. Unlike requirements, an unsatisfied hint must not cause a workflow engine to reject the process. Kept as its own reusable, $ref-able union so downstream profiles can narrow the set of accepted hint classes without depending on extensionPoints.