Plus the Baseline zone, which is required. So that gives a total possible BlueValues entries of 14, or 7 zones.
OtherBlues is an optional entry, so the Baseline zone should not be included when counting the number of potential zones, to avoid confusion. The maximum for OtherBlues is 10 pairs, or 5 zones, one or more of which can actually affect glyphs above the baseline.
Glyphs apparently has a way to determine which numbers go where (BlueValues or OtherBlues) based on the outlines. If not, then a Custom Parameter entry would be needed so the user can add them.
It would be very helpful to see the direction of the alignment zones too. A little upward arrow on the baseline zone, for example, to indicate that overshoots are pushed upwards there would quickly show if any of the values have the wrong polarity.
Well, it’s kind of necessary to understand the logic, if trying to set alignment zones. But as long as the directionality is clear it doesn’t matter to me whether it’s arrows, lines, stars or space rockets
Directionality of alignment zones is a tricky thing, because ‘top’ zones will actually pull nodes up to the upper edge of the zone. That’s also why the baseline zone is a top zone**, (overshoots need to be pulled up to the baseline). So I think displaying arrows on the zones may add to the confusion. +1 for lines on the ‘flat’ edge.
** or in PS Type 1 speak, a member of BlueValues instead of Other Blues