O.work.query()
Constructs a new object implementing the WorkUnitQuery interface.
function O.work.query(workType)
Create a work unit query object.
If the optional workType is specified, the query will find the given type of work unit. If the workType does not contain a : character, an exception will be thrown.
If workType is not specified, then you must either call ref() or tag() so that your query returns an acceptable number of work units.