Glyphs-Handbook-2013

Positioning of ghost hints (blue)
alongside regular stem hints.
A top ghost hint at position
100, and a bottom ghost
hint at position 50.
In the final OTF, all PostScript stem hints must be positive, i.e.,
have a width greater than zero. But even if you mistakenly
insert a negative hint, Glyphs will correct its direction at
export time, when all stem hints are turned positive.
8.3.2 Ghost Hints
You can use ghost hints when you need to vertically align the
top or bottom of a glyph but cannot apply a horizontal hint.
Take, for instance, a sans-serif uppercase I. The top needs to
align with the cap height zone, the bottom with the baseline
zone. In a serif I, you would apply horizontal hints to the
serifs, but the sans-serif letter lacks the horizontal features
necessary for a horizontal hint. In this case, you need to put a
top ghost hint on the top of the I, and a bottom ghost hint at
the bottom.
You can create a ghost hint by right-clicking on a single node
and choosing Add Horizontal Hint from the context menu.
Turn any existing hint into a ghost hint by right-clicking the
coordinate badge of a hint and choosing Make Ghost Hint from
the context menu. The badge of a ghost hint only displays the
position and its orientation. A downward arrow indicates a
bottom ghost hint, an upward arrow a top ghost hint. Attach
it to a point by dragging the blue circle onto a node. Toggle its
top / bottom orientation by selecting the hint and clicking on
the word ‘bottom’ or ‘top’ in the grey info box (View > Show Info,
Cmd-Shift-I).
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