Subject: Re: bug#65803: 29.1; Noto Sans Mono CJK JP has doubled-width on Windows

From: Werner LEMBERG <[email-masked]>
Date: Fri, 08 Sep 2023 14:49:11 +0000 (UTC)

> [...]  CJK fonts customarily contain tens of
> thousands of glyphs, of which only a small subset represent ASCII
> ``monospace'' characters relevant to Emacs, but the `tmAveCharWidth'
> field, which is derived from the font's OS/2 table:
> 
>   https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6OS2.html
>
> [...]

In general I recommend to refer to the OpenType specification

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

which is an ISO standard (ISO/IEC 14496-22 “Open Font Format”),
instead of the Apple-only TrueType reference.  There are significant
differences, especially for modern fonts.

    Werner