This is a boolean attribute which corresponds to the PROPBORDERLESS flag of
the PropInfo structure's Flags field (defined in <intuition/intuition.h>).
If this attribute is TRUE, the new propgclass object will not have a
border around it.  In an AUTOKNOB propgclass gadget, if the PROPNEWLOOK
flag is set as well (see the PGA_NewLook attribute), the knob will have a
3D appearance.