Enforce time tag for types ABSOLUTE, COMMAND_RELATIVE, and EPOCH_RELATIVE

[parkerabercrombie]

The documentation in the schema states (for the tag field of the time object):

Relative or absolute time. Required for ABSOLUTE, COMMAND_RELATIVE, and EPOCH_RELATIVE time tags but not COMMAND_COMPLETE.

However, this field is optional, so documents which specify ABSOLUTE time but omit the tag will still validate. Is it possible to enforce the tag when it is required?