Retrieves the children of a collection or the
attributes of a document. The children can be further filtered
by specifying an object query. The parameter array contains the
required elements 'objectIdentifier' and the optional elements
'attributeSelector' and 'objectQuery'.
The return value is an array of objects of type
HW_API_Object
or
HW_API_Error
.
See also
hwapi_parents()
.