Aligning text style properties with CSS?

[plehegar]

Section

https://www.w3.org/TR/epub-anno-10/#body

Describe the problem

This applies more to the EPUB annotations spec than the EPUB Annotations Vocabulary.

The specification defines a few text style properties, with associated keywords: color, highlight, textDirection.

The values for those properties are similar to a subset of properties and values defined in CSS: color, text-decoration, direction.

It seems to me that it would be beneficial for the long run to align the name of the properties (s/highlight/text-decoration/, s/textDirection/direction/) and also claim equivalence of values between the CSS properties and the EPUB Annotations, so that we don't introduce new values in EPUB Annotations that don't exist in CSS.

Describe the fix or new feature you propose

Align the name of the properties and point to CSS for the definition of each value used in those properties, eg 'pink' should point to https://drafts.csswg.org/css-color/#named-colors .

[iherman]

The issue of direction may be moot: we have a discussion on relying on the existing JSON-LD mechanism instead. See #2854, #2950 or #2967.

At the moment, reading systems have a variety of "themes" they offer for foreground/background, etc., with, in some cases, user settable values. The highlight colors, but even highlight styles, are often related to these themes. Setting some of these values in stone with fixed values does not seem to be possible, nor it is preferable in my view: choices in theme styling is one of the factors competing reading systems try to differentiate themselves.

I see two possible approaches:

• We refrain of using explicit names for, e.g., colors. After all, the only semantics we attach to these colors and highlight styles is to differentiate annotations from one another. They are pretty much like tags, except for a specific UI element. We may use some phantasy names or simply assign numbers to them.
• We add some sort of a disclaimer in the text which clarifies that these are approximate values only which are not meant to precisely define what "yellow" mean.

Personally, I tend to be in favour of the first option. Using "yellow" for a highlight color may be o.k. when the background is white, but may be less appropriate with dark background (where the font colour is often white-ish).