What are the required attributes of the `.null` glyph?

[bobh0303]

Description

Since v1.7, the COLR table description has included something similar to the following (quoted from v1.9.1):

Note: For fonts that use COLR version 0, some early Windows implementations of the COLR table require glyph ID 1 to be the .null glyph.

The .null glyph was described in the recommendations accompanying v1.7 spec, saying that it should have these attributes:

• glyph ID: 1
• name: .null
• encoding: U+0000
• contours: none
• width: zero

However starting with v1.8 the recommendations covering the first four glyphs were removed, which means there is nothing in that or subsequent versions that define the ".null glyph".

I'm guessing that the only characteristics of glyph 1 that are important to the early Windows implementations of COLR table are the contours and advance width — thus the glyph name and encoding are not important.

Is that correct? If so, could the spec be modified to read:

Note: For fonts that use COLR version 0, some early Windows implementations of the COLR table require that glyph ID 1 has no contours and zero advance width.

Page URL

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

Content source URL

https://github.com/MicrosoftDocs/typography/blob/live/typographydocs/opentype/spec/colr.md