OpenType 1.8.3 draft ready for review

[Peter Constable]

I’ve finished preparing the content for the next version of the OpenType spec, OpenType 1.8.3. Before publishing it, though, I’m offering a chance for review — please send any comments by August 21st.

Here’s a brief summary of what’s changed in OT 1.8.3:


  *   Incorporates comments on the DIS for ISO/IEC 14496-22 4th edition.



  *   The most significant technical changes are to the SVG table: these were developed in a joint effort among Microsoft, Apple, Adobe, Google and others. The motivation for the changes was that the spec was too loosely defined, and SVG+CSS is too vast, so without more specific guidance there was no likelihood of obtaining interoperability. These changes make the spec much more specific as to what must/should/should not/must not be used in fonts and supported in apps.



  *   A few other pages have significant, mostly editorial changes:



     *   OS/2: Previously, there were six separate changes, with a lot of redundancy but also some differences, and that was a pain to maintain. (If I change the text here, do I need to change it in the five other pages? What if the existing content in one of the other pages is different?) So, I’ve converged the six separate pages for versions 0 to 5 into a single page. Also, a few of the field descriptions are significantly revised:
        *   sTypo* metric fields, and usWin* metric fields: The changes were mainly motivated by some misunderstandings we had seen in some variable fonts being developed, leading to non-interoperable behaviours.
        *   fsType: The changes are to capture differences in the descriptions for different OS/2 versions. The wording for OS/2 version 0 to 2 were different enough from versions 3+ that might be read as contradictory, and having both in separate parts of the OT spec created ambiguity. The change attempts to give a single coherent and less ambiguous statement covering all OS/2 versions.

There’s also some additional guidance in the section on variable fonts regarding metric values — again, motivated by issues seen with some recent variable fonts — and the usLowerOpticalPointSize and usUpperOpticalPointSize fields — in response to questions from font developers.

See also some related changes in the Recommendations page.



     *   MATH: The whole page has been revised to improve clarity, and to apply editorial conventions that had been adopted in earlier OT versions but were not yet applied to this page. (No technical changes.)



     *   Baseline Tags: Some rewording for better clarity.


  *   There are some minor technical corrections in various pages, most or all in response to bug reports or comments on the drafts for ISO/IEC 14996-22 4th edition.



  *   There are a bunch of purely editorial changes. As I worked on the spec over 1.8, 1.8.1 and 1.8.2, I often encountered editorial inconsistencies, and I was constantly having to decide, “How should that be expressed and presented?” For some of these that occur repeatedly throughout the spec, I’ve made changes over these past few releases to bring consistency. This has what I think will be the last major batch of that kind of change: applying previously-adopted conventions to some remaining pages (e.g., MATH), and adopting a convention for how tag values (tables, features, etc.) are cited. (Inside single straight quotation marks? Double curly marks? No marks?)


A copy of the HTML/CSS content (in a .zip file) is available here, until August 21st:

https://1drv.ms/u/s!ApWD9Khdbmg5-8U2RTGSc3gb1pwLnw<https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2F1drv.ms%2Fu%2Fs!ApWD9Khdbmg5-8U2RTGSc3gb1pwLnw&data=02%7C01%7Cpetercon%40microsoft.com%7C7c4928aad79a48d92f7e08d5fe0d1f3b%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C1%7C636694254683443281&sdata=UINhWXpjFusaQGRpk%2B4Ex3OWK0v22QvFP5ZjlDUce5c%3D&reserved=0>

If you download and expand the .zip file, you’ll find an “opentype” folder. Inside that, there are two sub-folders: the “otspec183” folder has the OT1.8.3 content as it would be published, and the “otspec183_delta” folder has a copy in which files are marked up for insertions and deletions.



Thanks
Peter Constable
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