GF Check 130: Why is -20 the maximum italic angle?

Observed behaviour

Libre Caslon Italic gets the following “fail” message:

🔥 FAIL: Checking post.italicAngle value. - com.google.fonts/check/130 - 🔥 FAIL The value of post.italicAngle must be changed from -22.583 to -20. [code: >20 degrees]

However, the italic really does have an italic angle of more than 20 degrees.

I can’t find any specification that limits italicAngle to less than 20 degrees. The MS Typography spec for <post> simply says:

Italic angle in counter-clockwise degrees from the vertical. Zero for upright text, negative for text that leans to the right (forward).

I imagine this is just a sanity check … but calling it a “fail” seems like overkill.

Expected behaviour

If there is no documented problem with >20° italic angles, we should either:

A. Remove this as a check

or

B. Make the >20° check into an “info” check, if we think people may have set it incorrectly when it’s a high value. If this is the case, we might want to also adjust the message to reflect this objective – something like:

ℹ️ INFO The value of post.italicAngle is -22.583, which is significantly higher than most fonts. Check if the italic angle is set correctly. [code: >20 degrees]

[davelab6]

I think 20 is just made up as an absurdly high amount. Seems to be too low 😉

I think fail at 30 and warn at 20 is good. Should also check for negative values, if not already.

[davelab6]

Is there documentation of the distinctions between fail/warn/info/pass, especially in context of what’s expected for publication to the GFonts library?

I guess I have described it in the Typecon 2018 presentation deck but it does seem that this has not been properly documented. Let’s track in another issue.

Meanwhile, I made a PR to address this concern.