OpenType 1.8.3 published

Peter Constable

A new version of the OpenType spec — version 1.8.3 — has been published:

https://docs.microsoft.com/en-us/typography/opentype/spec/

While the content navigation links for the current version now all point to 1.8.3 pages, the previous version has been retained. I also managed to get OT1.8.1 migrated to the new site. (Maybe more can be added over time.) See the new Archived versions page:

https://docs.microsoft.com/en-us/typography/opentype/opentypeversions

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

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 but mostly editorial changes:

• OS/2: Previously, there were six separate pages for six versions, with a lot of redundancy but also some differences. That was a pain to maintain, and also confusing to use because the older versions had not been maintained in the same way. So, the six separate pages for versions 0 to 5 have been merged into a single page.
  
  Also, a few of the field descriptions are revised, notably the sTypo* metric fields, and usWin* metric fields; and there’s also some additional guidance in the section on variable fonts regarding metric values. These changes were mainly motivated by some misunderstandings we had seen in some variable fonts being developed, leading to non-interoperable behaviours. There’s also some additional guidance regarding the usLowerOpticalPointSize and usUpperOpticalPointSize in variable fonts, addressing questions from font developers.

• 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 review comments, bug reports or comments on the drafts for ISO/IEC 14996-22 4th edition.

After many years, the TrueType instruction content has finally been migrated from a Microsoft Word document and integrated with the rest of the spec! (Almost 20 years ago, that was said to be “in progress”.)

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. 

Complete details are provided in the change log:

https://docs.microsoft.com/en-us/typography/opentype/spec/changes

Thomas Phinney

Peter, thank you for your serious ongoing efforts on the OpenType spec. It isn’t a terribly thankful job, but your work will make a bunch of programmer’s and font folks’ lives subtly better, and they won’t even know what pain they avoided.

Dave Crossland

Really great to see this released! Thank you Peter!!!