Glyphs-Handbook-2013

Tip: If you do want to keep
a glyph accessible via two
dierent codes, it is better
to create a duplicate glyph.
10.3 DUPLICATE UNICODE VALUES
In some fonts, two or more letters erroneously carry the same
Unicode. If you try to import a font with double encodings,
Glyphs will warn you. Selecting all glyphs and choosing Update
Glyph Info from the Font menu will usually fix that problem.
In the reverse situation, where one glyph sports two
Unicodes, Glyphs will silently reset the Unicode value based
on the glyph name. The usual suspects for this are Delta and
(a.k.a. Laplace operator, glyph name ‘increment’). Omega,
name ‘Ohm’).
10.4 OPENTYPE FEATURE CODE
If all your features are auto-generated, you can usually fix
feature code troubles by re-compiling, i.e., clicking the Compile
button in the Feature tab of the Font Info window.
Glyphs tries to pass on any FDK compilation errors in
an error dialog. And it also tries to point you to where the
problem occurred by reporting the name of the problematic
feature and the line number. If it succeeds in doing so, the
error dialog will sport a ‘Show’ button. Click on it and Glyphs
takes you directly to the code problem. The following errors
may occur:
Contextual substitution clause must have a replacement rule
or direct lookup reference. You probably forgot or mistyped the
word ‘by’ in a substitution feature.
DFLT script tag may be used only with the dlft language tag.
You tried using a language tag without a preceding script tag,
e.g., if you use ‘language DEU;’, there needs to be a ‘script latn;’
somewhere before in the feature.
“Feature” statement allowed only in ‘aalt’ feature. You most
likely added your own feature code in the Prefix and forgot to
close a feature properly before starting the next one.
Glyph x not in font. You tried referencing a glyph that does
not exist. The error message will tell you which glyph it
was looking for in vain. You probably mistyped the name
of the glyph, accidentally deleted the actual glyph, renamed
the glyph, or forgot to create the glyph in the first place.
Sometimes, the automatically generated features are simply
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