OpenType Ordinals Feature - Best Practice

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Bhikkhu Pesala
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OpenType Ordinals Feature - Best Practice

Post by Bhikkhu Pesala »

On testing the OpenType ordinals feature of SourceSansPro in PagePlus, I found that every lowercase letter was superscripted, and not only those that followed a figure. I sent an email to Paul Hunt, who maintains the SourceSansPro font to ask why. This was the reply that I received:
The superscript letters are just that, superscript letters. These are
multipurpose and not particularly associated only with ordinals. Even if
they were intended as ordinals, it is too much work for the font developer
to add rules for every single language that might use ordinals. For this
reason, I have left the work up to the typographer to apply the feature
judiciously only where it is needed and not to an entire passage of text.
This is what we consider at Adobe to be best practice.
The Microsoft fonts like Calibri, Constantia, etc., are the same. So, both Adobe and Microsoft choose to ignore the recommended implementation for the OpenType Ordinals feature given in the Microsoft Tag Registry:
Recommended implementation: The ordn table maps various lowercase letters to corresponding ordinal forms in a chained context (GSUB lookup type 6), and the sequence No to the numero character (GSUB lookup type 4).
By using a chained context lookup, lowercase (and, optionally, uppercase) letters should be superscripted after any figures, including OldStyle figures, Tabular figures, etc.

Surely, this is a better way of implementing ordinals in a font, otherwise the user has to apply the ordinals feature to each instance of 1st, 2nd, 3rd, etc., throughout the document instead of just using it as part of a paragraph style.

Have I missed something, or is there a valid reason not to use a chained context? There is a superscript feature, so why bother with an ordinals feature at all if it is done as Adobe and Microsoft do it?
Ordinals Feature.png
Ordinals Feature.png (11.92 KiB) Viewed 4293 times
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