(1) ensure frame component or frame metric isn't used with clock time base;
(2) ensure frame component of clock-time expression is less than frame rate;
(3) ensure sub-frame component of clock-time expression is less than sub-frame rate;
(4) ensure seconds component of clock-time expression is less than 60.0;
(5) ensure minutes component of clock-time expression is less than 59;
(6) add tests and update documentation;