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Re(2): Expected behavior of CSSRule's setCssText.

From: Philippe Le Hegaret <plh@w3.org>
Date: Fri, 15 Sep 2000 17:30:38 -0400
Message-ID: <39C294FE.BA0E5AF9@w3.org>
To: Blaine Brodie <bbrodie@savagesoftware.com>
CC: www-dom@w3.org
> From: bbrodie@savagesoftware.com (Blaine Brodie)
> Subject: Re(2): Expected behavior of CSSRule's setCssText.
> [...]
> >
> >Setting this attribute will result in the parsing of the new value and
> >resetting of all the properties in the declaration block including
> >theremoval or addition of properties.
> 
> Yes, this description is good.

Too late for the next publication. I'll add the text before the REC.

> Can you please tell me what would happen
> in the following case where I retrieve a CSSValue from the rule's style
> declaration, and then make a call to the rule's setCssText method which
> removes the value's property from the declaration?  Does the outstanding
> CSSValue reference become detached from its parent rule and simply perform
> method calls on the old data [without affecting the rule's declaration
> values] or does the reference become invalid and invalid state exceptions
> are thrown on any of the value's method calls?
> Example.
>         styleRule.setCssText("H1 { ascent: 10 }");
>         CSSValue styleValue = style.getPropertyCSSValue("ascent");
>         style.setCssText("H1 {} "); //**** ascent property is removed eventhough
> a reference is outstanding ***//
>         ( (CSSPrimitiveValue)styleValue).getFloatValue();
> 
> Does the last call throw an invalid state exception or does it return the
> old value 10?

In that case, style.getPropertyCSSValue("ascent") will return null. The ascent 
property can be only applied on the @font-face rule [1].
Let me rewrite your example:
fontfaceRule.setCssText("@font-face { ascent: 10 }");
CSSValue fontfaceValue = fontfaceRule.getPropertyCSSValue("ascent");
style.setCssText("@font-face {} "); /**** ascent property is removed eventhough
                             a reference is outstanding ***/
( (CSSPrimitiveValue)fontfaceValue).getFloatValue();

Since the default value of the ascent font property is undefined, getFloatValue()
will return INVALID_ACCESS_ERR. But I certainly don't recommend this kind of
program
since this depends on the CSS property. Some CSS properties can be a CSSValue
or a CSSValue or a CSSValueList.
Let's imagine a property "foo" with the following definition:
 inherit | <integer> | <ident>+

Depending on the value, you'll cast the CSSValue in a different way.

It becomes a nightmare if you invoke setCssText on the CSS*Value* after the cast.
Some implementations can raise an INVALID_ACCESS_ERR, some others an invalid
state exception, this depend on your implementation. I'm not sure we want to
define
these corners cases. It will add more constraints on the implementation of the
interfaces and complexity in the spec for a bad practice.

I recommend to change your program if you really want to do that as following:

fontfaceRule.setCssText("@font-face { ascent: 10 }");
CSSValue fontfaceValue = fontfaceRule.getPropertyCSSValue("ascent");
style.setCssText("@font-face {} "); /**** ascent property is removed eventhough
                             a reference is outstanding ***/
if (fontfaceValue.getValueType() == CSS_PRIMITIVE_VALUE) {
   // this raises an INVALID_ACCESS_ERR since it is really a CSSPrimitiveValue
   ( (CSSPrimitiveValue)fontfaceValue).getFloatValue();
}


Philippe

[1] http://www.w3.org/TR/CSS2/fonts.html#matching
Received on Friday, 15 September 2000 17:30:56 GMT

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