this is mostly mean for the QQC2 apps running on PlaMo and using the Plasma style
to make them more close to the desktop style.
There is the enabledBorders property for PlasmaCore.FrameSvgItem, but for the Breeze style it does not draw any border, so maybe this change, if wanted, should be done on the style asset images?
Before patch:
After patch:
In the previous screenshots the style being used in Breeze, here it is with Air style, which draws the border from its assets:
and with this patch and still Air style: