Feature: Allow the creation of custom toggles that display over a canvas, similar to how the Layout Grid works.

I work with a development team, I design the look and they build it. The issue I have is sometimes the developers don't pay close attention to the spacing of my designs. Sometimes they will code a design element to be right up against a column when actually there should be a 20px padding. I think having custom toggles can help highlight these small details. I know/have workarounds to this minor issue but having an official feature for it would be great.

This idea also wouldn't be necessarily used for margins and padding. I see this can also be used to show hover states, overlaying text that describes functionality, or any graphic/text that can help the developer understand what the designer is wanting.