why are 'prop' tables bad?

[felipesanches]

The check com.google.fonts/check/unwanted_tables suggests removing 'prop' tables. What's the reason for this? The code currently does not report a reason for that. We should at least figure it out and clarify the message.

[anthrotype]

You mean "prep"?

[anthrotype]

Ha! "prop" the AAT table => https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6prop.html

[simoncozens]

Yeah, prop is bad because it's AAT; AAT was the Apple pre-OpenType way of doing font cleverness. It's OS X specific (although Harfbuzz now has optional AAT support), and it's old, so new fonts should not be doing that.

[khaledhosny]

There are a lot more AAT tables, why signal this one out?

[felipesanches]

I guess once one is flagged, the message has been successfully delivered to the user ;-)

Please open an issue with a longer list of tables to be rejected and we'll do so (only when reasonable, of course!).

[khaledhosny]

But it is not a particularly important AAT table, I can drop it and keep, say, morx or kerx tables and it would still be an AAT font that only works where AAT is enabled (or works differently).

Case in point this font is broken when AAT is supported and it does not have a prop table (only morx and feat).

[khaledhosny]

Code moved like a million times, but here is the commit that introduced this table and the issue that requested it. Nothing is mentioned about AAT and I doubt that ever was the reson, either the table was mistaken for another table or because FontTools didn’t support this table in 2016 someone checked a font with ttx and thought it is some junk table.