The code to calculate it is straight forward but I'm just curious as to "where this data is coming from"?. It's right there and I can't get my pythonic hands on it.
The tool help for it is bpy.ops.ui.editsource but the documentation doesn't reveal anything.
Should I be looking in the BMesh class?
Similarly: In object mode - the Transform Location is that of the last selected object. But the "pop up tool tip" at least gives me the "Slot Info"