Should there be some sort of validation of transitions?

Hi!

I was working on my Hiero plugin today and came across an issue when attempting to read the `transitions_test.otio` file in the sample_data folder.
In this file there is a cross dissolve between two clips that doesn't work in Hiero since there isn't enough media to create that dissolve.
To create a cross dissolve there needs to be overlapping media between them.
If you look at the file mentioned above in otioview you'll notice that the duration of *A* and *B* are both 50 and that *B* has a start_time of 0 in the source_range. AFAIK the dissolve between them would not be possible. Hiero won't accept it at least.
So my question is: Should there be added some validation logic for transitions to make sure they're usable in NLE's etc?

Start by inspecting sample_data/transitions_test.otio and viewing it in otioview, then compare the transition's media ranges with the behavior reported in Hiero. The issue needs a decision on whether validation belongs in OpenTimelineIO and what invalid transitions should do; done would require agreed behavior and coverage for this sample case.

Written by the indexing model from the issue text.