This is just a little time-saver for NLA-workflow. With the 'Auto-Blending' option
turned on in the Transform Properties (NKEY) for an ActionStrip, that strip's blendin/blendout values are determined based on the number of frames that the previous and/or next actionstrip(s) on overlap over the start and end of it.
It is turned on by default for new actionstrips added using the Shift-N hotkey.
Caveats:
* Only the actionstrips immediately on either side of the strip being evaluated, will
have any effect
* A strip that is longer-than, and extends over the sides of the strip being evaluated,
will have no effect
Additional Notes:
* Blendin/Blendout have been renamed In/Out in UI for brevity
* Button layout in NLA Transform Properties has changed slightly again, but hopefully that shouldn't be too much of an issue.
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