Standalone Lookups

Lookups written inside a feature block are applied when the feature is enabled by the typesetting system. Commonly, this is the intended behavior.

Some lookups, however, should not be applied directly by the feature. Instead, they are used as part of a different lookup, for example via a chaining substitution. In such cases, the definition lookup needs to be moved outside of the feature block. In Glyphs, this is done by writing the lookup definition in a Prefix section. However, since the Prefix code is placed before the Features code, and lookups are applied in the order in which they are written, such prefix lookups might get applied too early.

Resolve this issue by writing the standalone keyword before the lookup keyword when defining a lookup inside a feature. This will apply the lookup only when used from other lookups, while keeping the order of the lookup unchanged.

For example, the following is a stand-alone lookup being used as part of a chaining substitution inside the ccmp feature:

standalone lookup demo {
	sub gravecomb by;
	sub acutecomb by;
} demo;

sub @Uppercase @CombiningTopAccents' lookup demo;

For lookups defined outside of a feature, the standalone keyword is redundant and will be ignored.