Re: Attributes and enumerations

[Richard Tobin <richard@cogsci.ed.ac.uk>]

> "For interoperatibility, the same Nmtoken should not occur more than
> once in the enumerated attribute types of a single element."

> Does this mean I can't do the following?

> <!ATTLIST Options
>        Color (Yes | No) "No"
>        Bold (Yes | No) "No"
>        Italic (Yes | No) "No">

No, it means that for interoperability you shouldn't :-)

The interoperability in question is interoperability with SGML
parsers that don't conform to the WebSGML Annex of the SGML standard.
Since you almost certainly don't care about them, you can safely ignore
the advice.

("For interoperability" is defined in section 1.2 of the XML spec.
Strangely "should" is not.)

In case you're interested, the explanation for this particular warning
is that in SGML you can omit the names of attributes in certain cases.
For example, if you had

 <!ATTLIST font style (roman | italic) #IMPLIED>

you could say

 <font roman>

instead of

 <font style=roman>

(quotes aroung attribute values are also sometimes optional in SGML).
Obviously this wouldn't work if two attributes could have the value
"roman".  XML doesn't allow you to omit the attribute name so it has
no need for the restriction.

-- Richard