9.8.3.3 FD has wrong reference and is unclear which keys are "metric information only"

[petervwyatt]

Clause 9.8.3.3 FD, 2nd paragraph currently states:

The key for each entry in an FD dictionary shall be the name of a class of glyphs — that is, a particular subset of the CIDFont’s character collection. The entry’s value shall be a font descriptor whose contents shall override the font-wide attributes for that class only. This font descriptor shall contain entries for metric information only; it shall not include FontFile, FontFile2, FontFile3, or any of the entries listed in “Table 120 — Entries common to all font descriptors”.

All the metrics that should go in the FD sub-dictionaries are thus supposedly listed in Table 120. Looking back through old specs, ISO 32000-1:2008 references Table 122, which is also "Entries common to all font descriptors”, but section 5.7.2 of the PDF 1.6 spec (page 433) references Table 5.21, which is "Additional font descriptor entries for CIDFonts”, which makes total sense. Looks like there was a typo in the table number when transitioning the PDF spec to ISO.

[petervwyatt]

Technical questions:

• Is Table 120 CharSet key permitted or not? (it’s not “metric information only”)
• Are the required keys Type and FontName from Table 120 also required in this case? (Type and FontName are both not “metric information only” but they are required – or are they?)
• Is Table 120 FontFamily key permitted? (it’s also not “metric information only” but descriptive)

[petervwyatt]

Here is one proposed new wording:

The key for each entry in an FD dictionary shall be the name of a class of glyphs as defined in “Table 123 - Glyph classes in CJK fonts” — that is, a particular subset of the CIDFont’s character collection. The entry’s value shall be a font descriptor whose contents shall be a subset of the keys defined in “Table 120 — Entries common to all font descriptors” that override the font-wide attributes for that class only. This font descriptor shall contain entries for metric information only; it shall not include FontFile, FontFile2, FontFile3, xxxx see above - anything else?? xxxx or any of the entries listed in “Table 122 Additional font descriptor entries for CIDFonts”.

What is the "anything else"?

[lrosenthol]

Looking at well known implementation, the following keys in a font descriptor are processed:

Required

• Flags
• FontBBox
• StemV
• CapHeight
• Ascent
• Descent
• ItalicAngle

Optional (aka read if present)

• MissingWidth
• StemH
• XHeight
• Leading
• MaxWidth
• AvgWidth
• Style/Panose

[petervwyatt]

Just confirming - are you saying that your logic does NOT require the FontDescriptor required keys (Type and FontName from Table 120) as well?
If not, then they shouldn't be specified as required back in Table 120!

[lrosenthol]

That is correct concerning that implementation not looking at those keys.

However, they are required for other reasons. (remember, said implementation is not a validation tool...just a processor)

[petervwyatt]

Understood. So the solution will state that all required keys from Table 120 are required, as well as then explicitly listing various other keys from Table 120. The starting point for said "other keys list" is both your lists from above - subject to further suggestions or modifications by others.

[MPBailey]

I'm assuming Leonard missed anything obviously not a metric off his list (FontFile etc and everything that's better described as designers' metadata such as FontStretch). If so then I can confirm the same set here.