[ttml2] Loosen coupling between item name="usesForced" and forced

nigelmegitt has just created a new issue for https://github.com/w3c/ttml2:

== Loosen coupling between item name="usesForced" and forced ==
The "usesForced" named metadata item definition is very tightly coupled with use of `condition` in the document instance, in relation to the `forced` bound parameter. This means it cannot be used in other contexts that may define some forced functionality. See also the thread leading up to https://github.com/w3c/imsc/issues/311#issuecomment-361318848

Additionally, only one scope of usage is defined, at the document level. It would seem a reasonable optional usage to be able to scope it to an element in the body content such as `div` etc.

Since no processing semantic is based on the metadata item, there we can be less prescriptive about its usage. This will also have the effect of reducing the implementation and test burden.

Instead of the current wording:

> A boolean that expresses whether some `<condition>` expression makes use of the `forced` bound parameter, where the value adheres to `xsd:boolean`. If this named metadata item is present in a document instance, then it must be specified as a child of the `head` element.

I propose:

> A boolean that expresses whether some content within the specifying element's scope makes use of forced display semantics, where the value adheres to `xsd:boolean`. If this named metadata item is specified as a child of the `head` element then the applicable scope is the whole document; if specified as a child of a content element, then the applicable scope is that element and its descendants.
> Note:
> Forced display semantics can be expressed by use of the `forced` bound parameter within a `<condition>` expression. 

Please view or discuss this issue at https://github.com/w3c/ttml2/issues/609 using your GitHub account

Received on Tuesday, 30 January 2018 10:52:20 UTC