On the manual, the E key to stretch bone joints function is currently listed under the "Constraint Off" feature and should be corrected to the "Constraint On" feature.
Also, this E stretch bone key is a great feature, its shortfall is that its value can not be copied and pasted to other keys. I can't precisely make an animation loop if I want to replicate it from the first keyframe to the last keyframe when there are other keys in between. E + drag can only get your key to an approximate location with the screen coordinates off by a few decimal values. this results in unwanted popping in the animation loop at times.
I suggest maybe this E key function can become a toggle button in the property toolbar, then maybe it can be available toggled on or off when you are in the correct mode and precise coordinates can then be entered into the x and Y fields. also if it could be copied and pasted on the timeline would be super!
