Re: [csswg-drafts] [css-text-4] Make ideograph-alpha and ideograph-numeric part of text-spacing: normal (#6950)

The [`text-spacing: normal`](https://drafts.csswg.org/css-text-4/#valdef-text-spacing-normal)  definition is now:

`normal` -- Specifies the baseline behavior, equivalent to `space-start trim-end trim-adjacent ideograph-alpha ideograph-numeric`.

I am a little confused about the "baseline behavior.

Before ideograph-alpha and ideograph-numeric were added to `normal` definition, the meaning was clear to me, that is, the each value included in the definition of `normal` is the default value, so when we specify the text-spacing property partially changed from `normal` we can specify just changed values and omit values that are included in the `normal` definition.
For example, when just `text-spacing: trim-start` is specified, it implies omitted normal values, trim-end and trim-adjacent. i.e., `text-spacing: trim-start` was equivalent to `text-spacing: trim-start trim-end trim-adjacent`.

However, after ideograph-alpha and ideograph-numeric were added to `normal` definition, it is no longer that simple. Is `text-spacing: trim-start` equivalent to `text-spacing: trim-start trim-end trim-adjacent ideograph-alpha ideograph-numeric`? That will be useful when we want to change only trim-start/space-start/space-first behavior and keep other `normal` behavior, but if so, how do we change just ideograph-alpha/ideograph-numeric behavior from `normal`?

Then I decided to interpret it as follows:

- `text-spacing: trim-start` is still equivalent to `text-spacing: trim-start trim-end trim-adjacent`. The omitted default *-start/first, *-end, and *-adjacent are kept but ideograph-alpha and ideograph-numeric are turned off.
- ideograph-alpha and ideograph-numeric are turned on only when these values are explicitly specified, or `normal` (or `auto`, probably) is specified.

(I implemented it in Vivliostyle.js as per this interpretation. https://github.com/vivliostyle/vivliostyle.js/issues/1080)

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However this spec is not very clear and not very useful.

It would be better adding a new keyword, `no-interscript-space`, to turn off the interscript spacing.

The `ideograph-alpha || ideograph-numeric` part of the value definition becomes `[no-interscript-space | ideograph-alpha || ideograph-numeric]` and we can specify only this part to the text-spacing property when keeping other default (normal) behavior.




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Received on Saturday, 7 January 2023 09:24:35 UTC