Should host objects be able to have [[Class]] "Function", "Array" etc.?

Maciej Stachowiak mjs at
Fri Nov 14 20:56:12 PST 2008

On Nov 14, 2008, at 8:30 PM, Mark S. Miller wrote:

> On Fri, Nov 14, 2008 at 8:25 PM, Maciej Stachowiak <mjs at>  
> wrote:
> [...]
>  WebKit has a host class that is identical to the native String  
> class in every way, except that it compares equal to null and  
> undefined, vended in rare circumstances.[...]
> == or ===?


> Could you say more about this, or point at any existing docs?

Specifically, we expose a "filter" property on CSSStyleDeclaration, in  
support of the SVG filter CSS property. However, many sites test for  
"filter" to detect support for MSIE's proprietary "filter" property,  
which sadly has the same name but completely incompatible syntax.  
Thus, we return this kind of magical undetectable string so if tests  
don't detect us as IE.

It works basically the same ways as Mozilla's undetectable  
document.all, which we also support.

> Could this endanger any of the assumptions made by secure javascript  
> rewriters or verifiers such as Caja or ADsafe?

I wouldn't know, but I don't believe so unless such verifiers expose  
the CSS Object Model, in which case this is the least of their worries.


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