Hi Amelia,

The SVG WG and CSS WG revisited the error handling based on the discussions on 
this thread.


On Nov 14, 2014, at 4:08 AM, Amelia Bellamy-Royds 
<[email protected]<mailto:[email protected]>> wrote:

In summary, if the above resolutions are adopted, there will be four different 
error situations for filters:

  1.  If there is a syntax error or unsupported value in a CSS shorthand filter 
function, the filter property declaration will be invalid, and any filter 
specified earlier in the CSS cascade will apply.  This behaviour is defined by 
CSS error handling rules and can't be changed.

In case that the syntax for the filter property is not valid and does not 
follow the rules of Filter Effects[1] or other CSS specifications like CSS 
Units and Values [2], the specified filter value is disregarded and the no 
filter is set. The element is rendered as if filter was set to none. This is 
default CSS behavior.


  1.  If a URL reference in a filter property points to an inaccessible 
resource, or a resource that isn't a <filter> element, then the graphic will be 
rendered as if it had `filter: none` (In particular, it *won't* fallback to 
previous filter declarations).  This behaviour is defined in the new Filter 
Effects spec.

We resolved that if the element can not be found in the document or is not a 
filter element then the element is rendered as if filter was set to none.

  1.  If an SVG filter points to an inaccessible resource via an <feImage> 
primitive, work around it as best as possible (new resolution, sounds good to 
me).

The previous resolution is still valid. If the referenced input of feImage is 
not accessible take a transparent black image of the size of the subregion 
instead.

  1.  If an SVG filter has any other error, cause the filtered graphic to 
disappear (new resolution, justified as being consistent with current 
implementations, but not particularly useful otherwise).

If a filter effect references an input filter effect by identifier and there is 
no filter effect with the specified identifier or comes later in the DOM 
hierarchy then the filter chain is disregarded. The element is rendered as if 
filter was set to none.

The minutes can be found here: http://www.w3.org/2015/02/10-fx-irc

Greetings,
Dirk

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