numbers strike-through stylistic set

[axyz]

I have some general concerns about the SS02 stylistic set of the font.

Its goal is to provide an alternative way to strike numbers (as well as spaces and math/dividers symbols). Instead of showing the line overlapping the glyphs, there is a small transparent padding between the line and the glyph

My understanding is that the font file can only define the position and the tickness of the line-through, but it cannot define this "padding" style, nor change the line depending on the glyph it is on.

For those reasons, I assume this has been implemented in a "hacky", or at least controversial, way. Using a stylistic set completely replaces the glyphs with striked ones, but this has nothing to do with the text being actually striked trhough via markup semantics.

This leads to a number of issues:

• if the stylistic set is active and the text is semantically striked, there will be 2 overlapping lines visible
• if the stylistic set is enabled, and the text is not semantically striked, there may be a need to adjust accessibility roles to match what is visually shown with the intent
• if numbers with SS02 and regular striked text are next to each other, the "fake" line and the real one are not perfectly aligned
• standard markups will not be able to show the custom strike-through style, the stylistic set will need to be manually enabled on every text needing it

I wonder if this practice is acceptable for a public font, or if there are better alternatives to consider? Can kernings rules for example be aware of the presence of a strike-thorugh semantic and instead of operating on the line (not possible?) show glyphs with an empty horizontal space so that the line can fall in the middle of it leaving some space?

cc @afemartin

[RosaWagner]

First I must warn that Google Fonts doesn't support stylistic sets, so if the user intent to use the font from GF, the ss12 won't be accessible anyway.

The option with kerning, I am not sure to understand. In any case, there is no kerning between an automatic strike through and a glyph.

Otherwise, it would be possible the do the last option: having in ss12 glyphs with an empty space that correlates with where the strike through is supposed to be when activated.

But since we can set up the automatic strike through to overlap with the designed one through open-type, the overlap may not be visible. I can make a test.

[axyz]

First I must warn that Google Fonts doesn't support stylistic sets, so if the user intent to use the font from GF, the ss12 won't be accessible anyway.

Does that mean that the sets are stripped from the font file? Or simply not available via API options and/or in google docs and similar?

Would that mean that if we want to use the stylistic sets we'll not be able to use the font from the google CDN but host a non stripped version?

[axyz]

Otherwise, it would be possible the do the last option: having in ss12 glyphs with an empty space that correlates with where the strike through is supposed to be when activated.

But since we can set up the automatic strike through to overlap with the designed one through open-type, the overlap may not be visible. I can make a test.

That could be interesting to explore. In a way is still not great: the consumer need to make sure that the stylistic set is enabled only on elements that also semantically striked through, but on the other hand it could work better with screen readers and in general have correct markup...

One thing that may be challenging is that I think the custom line is intentionally not aligned with the regular one in order the be more centered on numbers, but we can check how much is the difference and if making the regular line slightly higher could be an option...
cc @gonzalo-ux

[RosaWagner]

Does that mean that the sets are stripped from the font file? Or simply not available via API options and/or in google docs and similar?

Would that mean that if we want to use the stylistic sets we'll not be able to use the font from the google CDN but host a non stripped version?

yes they subset all stylistic sets and other aesthetic features (oldstyle or tabular figures for example) to make the file lighter. You would have to host and use the font that I built for Zalando (the one for GF doesn't have a slant axis, but 2 VF, a roman and an italic)