A RoboFont extension to enable group spacing in the Space Center.
Supports importing and exporting spacing groups to .groupSpacing files.
Create left/right kerning groups using the Groups Editor.
Select a glyph in the Space Center and see all other glyphs in the same left/right spacing group.
Transfer the left/right margin of the current glyph to all other glyphs in the group.
Optionally, measure margins using the beam.