Clarify information sets cardinality of attributes.

[nigelmegitt]

Many elements permit {any attribute in TT Style Namespaces} or similar language. This test was taken from the initial element, as an example. Whereas for Content the cardinality is indicated, it is omitted for attributes. This could lead to the unintended interpretation that the text permits only a single attribute in the given namespace, rather than any number of such attributes.

Raising this and marking as agenda for discussion on the next call. Is there anything we can do to clarify this editorially in the TTML2 and TTML1 3rd Edition specs? For example append a * after the curly braces.

[skynavga]

We could add a note under conventions, but the use of curly braces follows the customary set notation, which means anything any the set. So a kleene operator * is not needed.

[nigelmegitt]

The wording doesn't say any attributes, it says any attribute, singular, which suggests only one is permitted. If {} means "any number of these" then we should certainly add that to the document conventions.

[palemieux]

In TTML1, we had {a single attribute in TT Style namespace}, which a contrast to {any attribute in TT Style Namespaces}.

[skynavga]

The convention used in TTML for specifying element information item syntax comes from [1]. In reviewing the usage there, I see a variety of instances of

{any attributes with non-schema namespace . . .}

So it would seem proper that we add change any attribute to any attributes. Note this is an editorial change only, since we have always intended "any attribute" to mean "any [one or more] attributes" in this context.

[1] https://www.w3.org/TR/xmlschema-1/