[whatwg] Accept full CSS colors in the legacy color parsing algorithm

Ian Hickson ian at hixie.ch
Fri Jul 15 11:43:25 PDT 2011

On Fri, 8 Apr 2011, Tab Atkins Jr. wrote:
> In the legacy color parsing algorithm 
> <http://www.whatwg.org/specs/web-apps/current-work/multipage/common-microsyntaxes.html#rules-for-parsing-a-legacy-color-value>, 
> steps 5 and 6 concern CSS color names - 'transparent' should raise an 
> error, and color names should be respected.  All other CSS color 
> syntaxes, though, such as the rgba() function, are just passed through 
> to the rest of the algorithm and appropriately mangled.
> This doesn't match Webkit's behavior.  Instead of steps 5 and 6, we just 
> try to parse it as a CSS color.  If we succeed, we use that color.  
> Otherwise, we chunk it into the legacy parsing algorithm and do what the 
> spec says.  So, for example, <font color=rgba(255,0,0,.5)>foo</font> is 
> actually displayed as partially-transparent red instead of dark green 
> (following the algorithm mangles the string into #050).
> Could we change those two steps to just say "If keyword is a valid CSS 
> color value, then return the simple color corresponding to that value."?  
> (I guess, to fully match Webkit, you need to change the definition of 
> "simple color" to take alpha into account.)

On Fri, 8 Apr 2011, Boris Zbarsky wrote:
> But it does match other UAs....
> Do you have web compat data here?
> I would much rather stick with color parsing as defined in HTML4 modulo 
> the "not a color name, treat it as a hex color even if it doesn't start 
> with '#'" quirk than replace the "is it a color name?" test with a "does 
> it parse as a CSS color?" test.

On Wed, 13 Apr 2011, Philip Taylor wrote:
> I don't know if this is relevant or useful but anyway: 
> http://philip.html5.org/data/font-colors.txt has some basic data for 
> <font color> values, http://philip.html5.org/data/bgcolors.txt for <body 
> bgcolor>. (Each line is the number of URLs that value was found on (from 
> the set from http://philip.html5.org/data/dotbot-20090424.txt), followed 
> by the XML-encoded value.)

Looks like there are values that would be affected by this change.

I've left it as-is. I think compat here is vastly more important than 
adding new capabilities, since this is only used for legacy features.

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
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