Thank you Terry for your response,
I have discovered a few things. I don’t think the blue triangles on the upper left and right corners are “grabable” like the white one in the lower left is. The cursor actually changes to a pointing finger with left/right arrows when you hover over the snap offset triangle, and when you move the cursor, the triangle moves with it and stays where you drop it. The upper triangles don’t move when you add a fade offset, but they DO change colors. If a fade has been set, the triangles are no longer blue, but white. They are cyan if a fade has been set, but you are zoomed out too far to see it.
I know this is nit-picky stuff, but I like to know what things are and why they change. I still can’t find it documented anywhere.
The downward pointing triangle on the interior top of a event appears to be an indication of the actual length of the media in the event. For example, if you drag the edge of the event to extend the event length (but not the media length), then this little triangle shows up to indicate media length.
More discoveries to come, I’m sure,
Charles