[css-logical] Flow-relative syntax for `margin`-like shorthands

[fantasai]

CSS currently assigns the values in the margin/padding/border shorthand to their physical longhands, i.e.

  margin: 1em 2em 3em 4em;

is equivalent to

  margin-top: 1em;
  margin-right: 2em;
  margin-bottom: 3em;
  margin-left: 4em;

I'm pretty sure we want some equivalent syntax for assigning into the logical longhands instead, but what should that be?

The current proposal is to put a keyword in front of the 4 values, like

  margin: relative 1em 2em 3em 4em;

Another possibility is to use a !keyword:

  margin: 1em 2em 3em 4em !relative;

or to create a new property in its place:

  margin-relative: 1em 2em 3em 4em;

or use some entirely as-yet-unused symbol or syntax.

And of course the exact keyword, if one is used, is up for debate as well; shorter would be better. People will be drawing up entire style sheets that use almost exclusively flow-relative properties, so this needs to be designed for comfort under frequent use.

Ideas welcome~

[chharvey]

I agree with the current proposal, a keyword in front of the values. I personally like relative better than logical, because I don't think this spec really has anything to do with "Logic" per se… (the study of truth and argument forms).

A couple of points:

1. the !relative keyword isn't already part of the standard CSS syntax and doesn't (and shouldn't) apply to all properties like the !important keyword does.
2. adding a new property like margin-relative would have to set (or reset) its sub-properties, but sub-property names are usually extensions of the shorthand. So a margin-relative shorthand would imply its sub-properties are things like margin-relative-block-start, margin-relative-block-end, etc. There are exceptions, though, in the case of grid-gap setting grid-row-gap and grid-column-gap—property names that still make me mad!

[MurakamiShinyu]

margins for logical shorthand -- is this bad idea?
I think plural word for shorthand makes sense, and columns is shorthand for column-* .

[chharvey]

@MurakamiShinyu — I see where you are going with this, but it could potentially become often confused with margin, which already exists. (Did they mean to put margins or was that a typo? Which one is relative again, I can't remember? etc etc…)

I think with a keyword such as relative prepended to the values, the code indicates very clearly and unambiguously what was intended—at the cost of just a few more bytes.

columns is okay because there is no column property, but in retrospect I would probably have preferred column for consistency.

[MurakamiShinyu]

I admit it's a crazy idea: 'margins' stands for "margin's writing-mode relative shorthand". But there is one advantage: 'margins' is easier to type than 'margin-relative' or 'margin: relative ...'. My concern is that people may feel troublesome to type a lot of 'relative' when css-logical-props becomes widely available.

[bradkemper]

I like the idea of !keyword that could be added to any 4-value clockwise shorthand (and their 3-value, 2-value, and 1-value versions). How about just an unadorned !, to make it an even easier, quicker switch? So...

border-radius: 2em 1em 4em / 0.5em 3em !;

is equivalent to

border-block-start-inline-start-radius:  2em 0.5em;
border-block-start-inline-end-radius:    1em 3em;
border-block-end-inline-end-radius:      4em 0.5em;
border-block-end-inline-start-radius:    1em 3em;

Adding the ! to a 1-value version, like margin: 0 ! wouldn't have any noticeable effect, but should be allowed.

[cork]

Why not go the same route as for box-sizing? So something like margin-mode: relative;

Then when the support gets common you could just do:

* { margin-mode: relative; }

div {
  margin: 1em 2em 3em 4em;
}

#exception {
  margin-mode: physical;
  margin: 1em 2em 3em 4em;
}

[SebastianZ]

Having a margin-mode property would go hand in hand with the current proposal of margin: relative 1em 2em 3em 4em;, i.e. be another longhand property for margin. The disadvantage of this is that its value infuences the handling of the other values, which might be unexpected.

I totally agree with @chharvey's comment that !relative (or ! for the same reason) and margin-relative have downsides.

Sebastian

[inoas]

If I got the ticket right (because the opening post doesn't really explain):

I think I have already answered via twitter... but I am suggesting transpose again.
And from an author point of view I would not care it it was margin-transpose: val val val val or margin: val val val val transpose;

[chharvey]

@cork I do like your idea of margin-mode. That way the syntax of the margin property would not have to change. The syntax of margin-mode would be

syntax:    [ physical | relative ] | inherit | initial | unset

initial:   physical

inherited: true

One upside would be that you wouldn't have to change the margin property when you want to change the mode—taking advantage of the Cascade, resulting in more readable diff.

Alas, a recent change of the spec indicates a different order when relative values are used.

p {
  margin: 1px 2px 3px 4px;
  /* equivalent to standard order (top, right, bottom, left)
  margin-top:    1px;
  margin-right:  2px;
  margin-bottom: 3px;
  margin-left:   4px; */
}
p.relative {
  margin-mode: relative; /* <-- added */
  /* equivalent to new order:
  margin-block-start:  1px; `top`    in LTR-TB
  margin-inline-start: 2px; `left`   in LTR-TB
  margin-block-end:    3px; `bottom` in LTR-TB
  margin-inline-end:   4px; `right`  in LTR-TB */
}

So in the example above, by adding margin-mode: relative;, you would still have to add margin: 1px 4px 2px 3px; in the second ruleset to keep things the same.

Another downside: you would have to have corresponding "mode" properties for the following, which could be a bit much:

• padding-mode
• border-width-mode
• border-style-mode
• border-color-mode
• border-radius-mode (related: [css-logical-props] border‐radius #491)

[MatsPalmgren]

I suspect margin-mode might be hard to implement - it's easier if you know at parse time how a property is supposed to be interpreted.

I like the !relative or ! proposal best so far. It would make it possible for multi-value properties to have both physical/logical values in the same declaration (if we want that). For example:
background-position: 10px, ! 20px, 30px, ! 40px;

I'm concerned though, that this might lead to new CSS properties being defined as physical-first and require ! for logical values. This would be unfortunate since logical values are superior in most cases. Perhaps ! could be interpreted as a general physical/logical switch though, so that for example grid-gap: ! 10px 20px; would set 10px on the longhand that corresponds to the vertical axis?

[MurakamiShinyu]

I like the idea of #1279: margin-block is shorthand for margin-block-start + margin-block-end, and margin-inline is shorthand for margin-inline-start + margin-inline-end.
These will be often more useful than single margin flow-relative shorthand, and I am ok with adding 'relative' keyword when the margin shorthand is needed. Or how about the following syntax:

  margin: [ block <'margin-block'> || inline <'margin-inline'> ]

e.g.

  margin: block 1em 3em inline 2em 4em;

[inoas]

I have to raise my voice and say that short symbolic like a punctuation (!) mark are really not good practice IMHO. The gains in saved typing are minimal and the symbol does not transport its meaning. It pretty much feels regexpy and IMHO CSS should not be.

I'd favour extra logical properties. Aka margin and padding are absolute and margin-relative and padding-relative are not (dimensions for position and dimensions-relative or similar could be added later).

That is a very clear and easy interface for authors and there is no clash between old properties and new properties. Authors can also use margin and margin-relative independent of each other and thus are not breaking css parsing of older browsers!

So I really like @fantasai initial proposal.

[fantasai]

Wow, okay! Here's some responses:

• I think it's pretty sure we are not doing a separate property to control interpretation of shorthands. First, as @MatsPalmgren mentions, this is harder to implement--we really want a switch that's syntactically part of the declaration and lets us handle this at parse time. Secondly, it creates an "action at a distance" effect, which is likely to result in confusion and errors as multiple parts of a stylesheet interact.
• Agree that margin vs margins is going to be confusing and we shouldn't go that route. :) For languages that pluralize with s such as English, it's a mostly-unnoticeable morpheme and not something we ever want to be a distinguishing factor in any CSS syntax.
• I agree with @inoas that using just ! alone is likely a bit too obscure (and also a bit too general, imho, as we use !keyword for other things like !important). However, I also agree with the concerns about !relative or relative or -relative potentially being too much of a typing burden; as I mentioned in the OP, we do expect this to become the default mode of assignment for many authors, so I'd say it's fair to trade a bit of obscurity for a bit of typing efficiency.
• Wrt @MatsPalmgren’s comment about moving to flow-relative directions... new CSS models like Grid and Flexbox tend to use flow-relative directions to begin with, however for anything that's analogous to an existing CSS feature like margin or background-position, consistency is a more important consideration. Hence scroll-snap-margin is physical, even though we would have preferred it to be flow-relative.
• transpose is not a bad name, the main downside is that it doesn't indicate what the mapping is! There's a distinct possibility that more mappings could be added in the future--Writing Modes already includes both flow-relative and line-relative mappings.
• Fwiw, margin-block and margin-inline were resolved to add already, I just forgot to make the edits. :( I'll go do that now. ;)
• Wrt interleaving keywords... one of the great things about the 4-value shorthand syntax is the way that it can use 1, 2, 3, or 4 values to assign to the four sides, and pairs things up in ways that both correspond to common use cases and yet also unroll syntactically in a consistent way. I think we want to keep those qualities; and also be consistent with Grid which already has a 4-value shorthand in grid-area.

[MurakamiShinyu]

Agree with @fantasai. Now I feel original relative keyword or -relative suffix were better. However, I think the word relative also has obscurity. People may think the relative is related to position: relative, and may not notice that it is about "flow-relative-directional".
(For this reason I think logical keyword might be better then relative)

How about margin-bi (suffix -bi, stands for "block and inline")? I know this is exceptional in CSS property naming convention (avoid abbreviations and use complete words), but has the following advantages:

• easy to type, only three additional characters to the original name
• we have *-block and *-inline properties, and making the combined shorthand names using the first letters of "block" and "inline" will be easy to understand
• "bi" indicates the order of values, block is first then inline, and convenient to remember the value syntax

and CSS already has abbreviations in some keywords, e.g., "rl" (for "right to left direction") in vertical-rl value of writing-mode, and using "bi" for "block and inline directions" will be not too bad.