Change object reference point for more flexible positioning (easy symmetry)

[zalexzperez]

When we are looking to achieve symmetry in our designs, a distance measurement tool can come in handy.
Consider this example as reference:

The horizontal red lines are the same length, revealing the two buttons, identical in width, are not positioned exactly at the same distance from the borders.

This tool, however, would only help during inspection. These two questions arise:

How could be achieve this symmetry without manual coordinates calculation?
How could be keep this symmetry if object width later changes?

Being able to change the object's reference side (and the display's reference side) would tackle this problem.
For example, if we wanted to make the button's right side 212px from the right border of the display, we'd set it like this:

The opposite symmetrical button would take the same value but use the default Left reference.

Same thing for vertical positions (Top / Bottom references).