Horizontal space to leave between related widgets.
Each section should use these values for spacing its widgets.
For example, you can use +/- HSPACE as the offset of a left or
The tabbed property composite also inserts VSPACE pixels between
section composites if more than one section is displayed.
Space to leave between the center of the property tab and the closest
widget to the left or right. I.e. for a property tab whose widgets are
logically divided into two halves, the total space between the halves
should be 2*CENTER_SPACE.