Glyphs adding ID18 to fonts

Hi there!
I’m working on a large family where fonts can have rather long names (widths, weights, italics).
My understanding is that ID18 is needed when ID4 is too long, but that it can cause cross platform issues. My strategy has been to use shortened names for setting ID4 so that it doesn’t exceed 27 characters, and not setting ID18 at all.
I’ve noticed that for all fonts that have an ID4 longer than 25 characters, Glyphs will automatically add an ID18 to the name table.
Do you confirm that it is intended behavior? Was my assumption of 27 chars being the limit wrong?

Bonus: I usually let Glyphs build ID6 itself, but noticed it never uses short names. I’ve read that if ID6 > 27(29?) chars it can also cause issues. Should I add a postscripFontName using the shortened names I use for ID4 or can I safely let Glyphs do its thing?

Some of the issues are backdating to pre-OpenType times. Today, it may still be an issue with ancient printer drivers.

Name Table, ID 6:

PostScript name for the font; Name ID 6 specifies a string which is used to invoke a PostScript language font that corresponds to this OpenType font. When translated to ASCII, the name string must be no longer than 63 characters and restricted to the printable ASCII subset, codes 33 to 126, except for the 10 characters ‘[’, ‘]’, ‘(’, ‘)’, ‘{’, ‘}’, ‘<’, ‘>’, ‘/’, ‘%’.

In a CFF OpenType font, there is no requirement that this name be the same as the font name in the CFF’s Name INDEX. Thus, the same CFF may be shared among multiple font components in a Font Collection. See the ‘name’ table section of “Recommendations for OpenType fonts” for additional information.

63 characters is the limit. For supporting legacy hardware (and making legacy EOTs work), you may want to make sure that the first 29 characters are unique. But really, these are edge cases.

BTW I just updated the Naming tutorial with the wording conventions from the latest OT Spec version. Some of the entries have new names now.

Hey Rainer!
Yes, I’ve been getting my info from the Microsoft specs so I wasn’t too bothered with ID6, just wondering if anyone had experienced any other potential issue :wink:

About Glyphs adding ID18, do you confirm thats its triggered by ID4 being considered too long by Glyphs (even though thats shorter than the 27 chars I thought were in the specs)?