[css-text] text-spacing is very complicated

[litherum]

text-spacing is getting very complicated now. By my count, the current grammar accepts 769 different combinations of values (770 if you count auto). It's probably worth an investigation to determine which of these combinations are actually useful.

[frivoal]

There probably are a number of unnecessary combinations in there indeed. We should get help from JLReq to figure which ones are essential.

cc: @r12a @macnmm @fantasai @MurakamiShinyu

[MurakamiShinyu]

I think that the text-spacing property is like a short hand property such as font-variant whose total number of combinations is very large and hard to reduce.

[litherum]

@dauwhe mentioned that Prince has something similar (prince-text-replace?). Perhaps he has some insight into how to better design text-spacing.

[dauwhe]

Here's the PrinceXML property in action. It finds a period followed by a space, and replaces it with a period followed by an em-space (U+2003). PDF of the result attached.

p.space {
  prince-text-replace: ". " ".\2003";
}

This has lots of problems, not least because you can't define under what context the replacements happen.

prince-text-replace.pdf

[kojiishi]

How about considering splitting into multiple longhands? I recall that was the original plan of @fantasai when this property gets more matured?

As suggested in #4246 (comment), similar to font-variant, having multiple longhands allows authors to change one of them without changing other values, such as enabling/disabling just ideograph-numeric oly for some text, or disabling no-compress only for a span.

Doing so might also address #7183, and it looks like there's a mild consensus on in at TPAC. /cc @r12a

For implementers, testing the parser for the 770 combinations of values without errors is not an easy task. Splitting to multiple longhands and using the existing already-tested mechnism for shothand helps.

[macnmm]

The JIS standard defines a set of character classes and their relationships in terms of a spacing range and compression/expansion priority, but there are problems with how these classes are defined (not differentiating between proportional/half-width/full-width for example) as well as no consideration of mixed script text. We need a modular approach that defines the character classes, the spacing ranges (with priority) of each class pairing, according to the needs of the UA and how fancy it wants to be when supporting complex layout. A reasonable default behavior could also be proposed as part of the jlreq, I would hope, so the spec could then be about a sparse override of the default.

[litherum]

Agenda+ to discuss the possibility of splitting up the property into longhands (just like how we did with text-decoration-skip)

text-spacing is something we’d like to start implementing soon (weeks not months).

[r12a]

Note that, if nothing else, i'd very much like to split out autospace from text-spacing. See #7183. Can we please bring the discussion in that issue to the agenda along with this issue?

[frivoal]

@litherum I just did propose longhands for text-spacing as well in #8288 (comment) curious to see if you agree about the particular design proposed.

[fantasai]

OK, so @florian and I did some brainstorming, and here's a simplified version of text-spacing and possible longhand expansion that tries to address the comments in #8288 #7183 #4246 #8263 #318

Summary:

text-spacing: normal | none | auto | <'text-autospace'> || <'text-spacing-trim'>
  text-spacing-trim: auto | space-all |  trim-all | [ allow-end || space-first ]
  text-autospace: normal | auto | no-autospace |
                  [ ideograph-alpha || ideograph-numeric || punctuation ]
                  || [ insert | replace ]

Fullwidth Punctuation Trimming

text-spacing-trim (or text-spacing-full-width):
    auto | space-all |  trim-all | [ allow-end || space-first ]

This controls the spacing or trimming of fullwidth punctuations at the start, end, and adjacent positions. [ allow-end || space-first] are variations on trim-all. We don't think that there's a real need for these two values in combination with space-all, or with any other mix of the existing keywords; but if we wanted to allow the full combinations, we could insert them all here. The initial value is under debate in #2462 (and will likely be space-first).

Interscript and Punctuation Space Insertion

text-autospace:
    normal | auto | no-autospace |
    [ ideograph-alpha || ideograph-numeric || punctuation ]
    || [ insert | replace ]

The initial value would normal (currently defined as ideograph-alpha ideograph-numeric).

(punctuation is for languages like French, which want a narrow non-breaking space before ;:?! and an normal non-breaking space on the inside of « and ».)

To address one of @r12a’s requests in #7183 (split out as #8263), insert inserts spaces where there aren't any (as currently specced) while replace will do the same as insert, but also replace incorrect spaces (U+0020 and U+00A0) with correct spacing.

Compression Control

text-justify: <current-stuff> || no-compress

This moves no-compress into the text-justify property, which is the “how do I justify” control. It would not be reset by the text-spacing shorthand, which is probably better.

Shorthand
The shorthand for these would be:

text-spacing: normal | none | auto | <'text-autospace'> || <'text-spacing-trim'>

normal sets both to their initial values; none maps to no-autospace space-all (which is the “do nothing” value appropriate for e.g. monospace text, or to avoid compat issues with fiddly legacy content).

---

Excess Longhands
It might be reasonable for the two functions of text-autospace to cascade independently, so it could have further longhands (names TBD):

• text-autospace-style: normal | no-autospace | auto | [cjk-alpha || cjk-num || punctuation ] with initial value normal
• text-autospace-mode: insert | replace with initial value insert

text-spacing-trim could also have further long-hands as described in #8288 (comment), with a full explosion of possible combinations. However, these seem unnecessary (as most combinations aren't actually useful) and possibly a cascade footgun (if authors try and tweak something on top of an assumed base behavior using a longhand, without noticing that the other longhands have a cascaded behavior different from what they assumed would be there as the base behavior).

[r12a]

@fantasai i think this is a step in the right direction. I'm still trying to find the time to finish drilling into the detail fully, but one thing i did notice is that there appears to be no way to set the width of the gap introduced by autospace. That turned out to be something that content authors had different opinions about, or may use different widths in different contexts.

[SebastianZ]

text-spacing: normal | none | auto | <'text-autospace'> || <'text-spacing-trim'>
  text-spacing-trim: auto | space-all |  trim-all | [ allow-end || space-first ]
  text-autospace: normal | auto | no-autospace |
                  [ ideograph-alpha || ideograph-numeric || punctuation ]
                  || [ insert | replace ]

I assume text-spacing: auto is equivalent to text-spacing-trim: auto and text-autospace: auto, right? If so, it doesn't have to be explicitly defined for the shorthand in the current syntax.

Sebastian

[r12a]

one thing i did notice is that there appears to be no way to set the width of the gap introduced by autospace.

I'm guessing that that may be because the French use case may require more than one width in the same paragraph?

insert inserts spaces where there aren't any

I suggest using the word 'gap' for what is opened up by autospace, rather than 'space'. That will probably avoid a certain amount of confusion. So that quoted text would read "inserts a gap where there wasn't any".

[fantasai]

OK, we've edited in the refactoring described in #4246 (comment) as resolved by the CSSWG, along with the suggestion to rename trim-all to trim-auto per @MurakamiShinyu's #4246 (comment).

Follow-up issues filed:

• [css-text-4] Add 'text-spacing: trim-all'? #8482 referencing @MurakamiShinyu's comment about introducing a trim-all value for handling number formatting etc.
• [css-text-4] Specify width of autospace gaps #8510 referencing @r12a's comment about specifying the width of autospacing
• [css-text-4] text-autospace: what gets copied? #8511 referencing @r12a's comment about copy/paste operations

Please file additional follow-up issues if anything else needs fixing. Thanks!