These two functions test for clear and set to clear, respectively, the property named <prop-name> on the given <object>. If <object> is not valid, then E_INVARG is raised. If <object> has no non-built-in property named <prop-name>, then E_PROPNF is raised. If the programmer does not have read (write) permission on the property in question, then `is_clear_property()' (`clear_property()') raises E_PERM. If a property is clear, then when the value of that property is queried the value of the parent's property of the same name is returned. If the parent's property is clear, then the parent's parent's value is examined, and so on. If <object> is the definer of the property <prop-name>, as opposed to an inheritor of the property, then `clear_property()' raises E_INVARG.