This function will return
true() if and only if both edges of the global selection are in a node, or in a descendant of a node.
Thus, it will return true in the following cases:
A | B / \ C D / \ E F <----- Selection end, in C, just after F ^---- Selection start, in C, just before F
This function will invalidate itself when the selection is moved to outside or to inside a node. It can also be used to assign different families to an element depending whether it contains the selection or not. Mind performance when doing this.
The node to check
Whether the selection is inside that node