Error Processing should talk about when to use initial values for attributes

[heycam]

The current https://svgwg.org/svg2-draft/implnote.html#ErrorProcessing section doesn't refer to initial/invalid values of attributes, so it's not exactly clear that you're meant to use them when an attribute is invalid in some way. For example looking at https://svgwg.org/svg2-draft/coords.html#ViewBoxAttribute it says that negative values for width/height inside the viewBox are an error, but the Error Processing section linked to doesn't make it clear that the behaviour should be as if the attribute weren't specified (as that's what's specified for the "initial value" in the grey attribute definition box).

[sideshowbarker]

See https://www.khronos.org/registry/vulkan/specs/1.0/xhtml/images/tstripadj.svg for a case where this results in different behavior between Chrome and Firefox due to differences in what they do when they run into a (invalid) negative viewBox value.

[philiptaylor]

The image linked above got fixed, the broken original is at https://github.com/KhronosGroup/Vulkan-Docs/blob/d204ac2f6991f75fab2ebc22136fd179d692f84f/doc/specs/vulkan/images/tstripadj.svg

[nikosandronikos]

3.2. Attribute syntax does note the following

The Initial value column gives the initial value for the attribute. When an attribute fails to parse according to the specified CSS Value Definition Syntax, ABNF or EBNF grammar, or if parsing according to the URL Standard or by the prose describing how to parse the attribute indicates failure, the attribute is assumed to have been specified as the given initial value.

So I think we should just remove the link to 'Error Processing'.

[nikosandronikos]

We might also just want to check that viewBox is clear about throwing the whole viewBox away if one parameter isn't correct.