[css-text] `trim-both` and `trim-start`

[xfq]

https://drafts.csswg.org/css-text-4/#text-spacing-trim-property

Recently, while discussing text-spacing-trim in CSS, the clreq TF felt that trim-both and trim-start are quite similar.

The behavior of trim-start in certain cases appears to be counter-intuitive. For instance, if there isn't enough space remaining at the end of a line, the content might be pushed to the next line. This could trigger a line-breaking rule (such as preventing a closing quotation mark from appearing at the start of a line).

And there is a high probability that three full-width characters would be pulled down to the next line (since a paragraph ending with a closing quotation mark typically includes a sentence-ending punctuation mark immediately preceding the quotation mark).

Is there any specific scenario where trim-start is absolutely essential?

[frivoal]

You are right, they are very close, and I would agree that in the general case, trim-both is a better/safer value.

I think the main useful difference comes whenusing justification: trim-both will give a flush right edge, while trim-start will visually have a 0.5ic gap at the end of lines where the last character is a closing punctuation. This may seem like another argument in favor of trim-both, and to some authors it will be, but if you have sized your lines to be an integer number of characters, removing that gap means you need to distribute in throughout the line, which can break the visual grid-line alignment of characters.

Authors who don't care about that will be better served by trim-both I think, but some may, so offering it as a choice seem useful. At least that's what I think the reason for having both is.

If we don't really care about that, I think I'd agree that trim-both is enough, and that we could remove trim-start.

[xfq]

@kidayasuo Any input from jlreq TF?

[r12a]

If we don't really care about that, I think I'd agree that trim-both is enough, and that we could remove trim-start.

Except that trim-start is supported by Blink, but trim-both is not (see https://w3c.github.io/i18n-drafts/articles/styling/inline-space.en.html#punc_initial_nospace — early draft !). That means we'd lose part of the little behaviour that currently works. :(

But i have to say with the clustering of behaviour around these keywords, rather than having separate properties for paragraph-initial, line-initial, line-final, and punctuation-sequences is really hard for content authors to get their heads around the differences and which to use. Plus, i got the impression that there may be gaps, eg. for Traditional Chinese behaviour, that are not covered. I'm inclined to raise an issue to propose splitting them apart.

[r12a]

See #13789