Rotating an edge around another without stretching edges How do I go about rotating an edge around another while keeping all edge lengths the same? 

On the included screenshot, I'd like to move the orange edge freely around the white edge without any edges changing lengths. So, the white edge should simply be the pivot.
In the Pivot Point menu, select Active Element, then do the rotation (around the Y axis in this case, so R/Y)

The Active Element is the last selected element, it appears in white instead of yellow.