coding

Lookup calls and lookup types

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I think I'm getting to grips with OpenType coding - I just birthed my first contextual one-to-many substitution, and am as proud as you'd expect - but I'm still puzzled by one thing and unsure about another.

The puzzle is that when I define-and-run a lookup, the layout engine goes back to the start of the glyph run, as I'd expect. But when I call a lookup, it doesn't, at least in FontLab. Is that just how it is?

The uncertainty is over whether all kinds of lookup types are allowed in all features, or whether it's better to stick to the lookup types specified for features at [[http://www.microsoft.com/typography/otspec/features_ae.htm|the Microsoft OT spec site]]. I know FontLab is liberal, but are all apps?

Thanks very much for any help!
George