Allow initial style to be constrained to an element type?

[nigelmegitt]

Whereas some style attributes, such as tts:backgroundColor apply to multiple types of element, e.g. region, div, p etc, only one value of any style may be specified in the initial element. This means it is not possible, say, to set the initial value for tts:backgroundColor only as applied to span elements.

Would others find it useful to be able to specify this semantic?

[skynavga]

My initial thoughts come down to:

• The initial values for style definitions are currently defined in a global scope, without any constraint as to application. This is consistent with XSL FO and CSS.
• Adding a constraint such as element type begs the question of what other type of selectors might apply, and soon we may have full blown XSL selectors, e.g., an element of a given type that is a descendant of an element of another type that has an attribute of certain value, etc. A slippery slope.
• This would require a substantial change to the style resolution algorithm.
• As this is a new feature, it would need new Schema support as well as new feature designators defined; in other words, a new profile. In the past, we agreed to put new features into the next major revision, which at the moment is TTML3. Has that changed?

Overall, I wonder if this level of effort is justified by introducing what is essentially a convenience mechanism for authoring tools that could do this another way that already exists, i.e., assigning styles directly to the affected elements (in whatever rich context the authoring tool sees fit).