I am working on a typeface and I notice these small red rectangles below several glyphs in FontLab.
Can anyone tell me what this indicates? See attached image below.
It means someone else has already designed a glyph just like yours.
Actually, it means that the glyph is the key glyph in a kerning class.
(RTFM, by the way. Took me only ten seconds to find the answer by looking there.)
RTFM indeed. Thanks, Mark.