On Aug 28, 2006, at 9:00 AM, Jim Grandy wrote:
> On Aug 26, 2006, at 6:02 PM, Adam Wolff wrote:
>
>> On Aug 23, Jim Grandy wrote:
>> [snip]
>>> I guess my preference is to choose simplicity over symmetry, and
>>> declare
>>> that $style constraints are always interpreted as strings.
>> This would make the $style feature almost useless. Most LFC functions
>> (like setWidth) behave erratically if you hand them strings. We
>> could have
>> a policy of trying to convert strings to numbers, but it might
>> produce
>> unexpected behaviors with, say, hex values.
>
> Yeah, you are right. After thinking about this over the weekend, I
> think I was pushing CSS-purity a bit too far into the client side.
> After all, HTML "user agents" reinterpret CSS values as e.g. color
> values, single font names, etc., so we should be able to do the same
> at the intersection between the CSS engine and LZX. (I'm also now
> fine with $style being an expression constraint, especially if (as
> ptw asserts) all constraints are currently expressions. Again, I was
> carrying CSS-ness too far into the client.)
>
> I haven't gone and tracked down the source of the constraint syntax
> (does anyone have a reference?), but it seems to me we could add a
> type declaration to all constraints and solve this problem as well as
> the bigger problem of constraint type coercion. Perhaps using a colon?
>
> $style:number{'font-size'}
>
> Then for ordinary constraints it would collapse:
>
> $:color{"#" + parent.red + parent.green + parent.blue}
>
> Just throwing out a possibility; maybe someone already has a proposal
> for constraint type coercion that we could revive?
>
> But for style constraints, there's a verbosity problem: we know that
> e.g. font-size is always going to be a number, so maybe there's a way
> of declaring the default type of a CSS property. Not sure where that
> would be declared, unless we only support it for built-in style
> properties and it's internal to the compiler.
>
Complicating matters further:
Lengths in CSS can be expressed in several units:
12px
1em
97%
12pt
Similar unit options for other "types".
And there's the amazing shorthand mechanism -- from section 1.4.3 of
http://www.w3.org/TR/2006/WD-CSS21-2006041
> 1.4.3 Shorthand properties
> Some properties are shorthand properties, meaning that they allow
> authors to
> specify the values of several properties with a single property.
> For instance, the ’font’ property is a shorthand property for
> setting ’font-style’,
> ’font-variant’, ’font-weight’, ’font-size’, ’line-height’, and
> ’font-family’ all at once.
> [snip..]
> h1 { font: bold 12pt/14pt Helvetica }
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