Dynamic Outsides automatically adjusts the Outside size by changing the Border Size to zero.
Dragging a new opening to the edge of the mat will adjust the outside size by adding the Border Size around the Bounding Rectangle of the existing openings.
The Border is the area of precisely definable width between the outside edge of a Mat and the edge of the Opening(s) in the Design Editor, Nesting, and Visualization.
The Bounding Rectangle is a dotted or invisible rectangle that encompasses the outermost boundaries of the selectedobject(s) in the Design Editor and Trace, and includes Control Points which can be used to edit the object.