When transforming video sequencer handles, there are limits beyond which you cannot move them which is enforced by the transform code.
The Slip operator ignores these constraints - allowing the strip content to be dragged with offsets that are outside the strip start/end.
- Start a new Video Sequencer Template
- Add a new scene
- Add that scene as a sequence strip.
- Press 'S' to slip the selected strip.
- Move the strip to the right of the strip (500 frames eg) so the strip has no content in it.
- As an example of how this isn't properly supported:
- Change the "Strip offset start" - The Scene flips and becomes negative, showing handles in the opposite directions.