Enumeration: symbol combine

Specifies how symbol shapes are combined with those below it

--Script syntax--
In scripts, symbol combine modes are passed around as a string.

--Possible values--
The value is one of the following options:
! Value			Description
| @overlap@		Place this shape on top of those below it.<br/> Further combine options only apply to this shape.
| @merge@		Marge this shape with the one below it, they are considered a single shape for further combining.
| @subtract@		Subtract this shape from the one below it.
| @intersection@	Take the intersection of this shape and the one below it, only areas that are in both shapes remain.
| @difference@		Take the difference of this shape and the one below it, only areas that are in exactly one of the shapes remain.
| @border@		Use this shape as additional border for the shape below it.

--Examples--
> combine: overlap
