Re: Difference for attribute values

[James Clark <jjc@jclark.com>]

> Let me reformulate my question.  Do we allow
>
> <difference> <datat type="xsd:short"/> p1 p2 ... </difference>
>
> ?

Let's consider this in terms of the grammar I posted.  If we added
<difference> then the unrestricted grammar for pattern would simply get
another choice:

  | <difference> pattern pattern </difference>

For the restricted grammar, I think the right thing to do is to change
things as follows:

value ::=
    string
    | <list> tokens </list>
    | <list> <empty/> </list>
    | <choice> value value </choice>
    | <choice> <empty/> value </choice>
    | <difference> value value </difference>

tokens ::=
    token
    | <text/>
    | <oneOrMore> tokens </oneOrMore>
    | <group> tokens tokens </group>
    | <interleave> tokens tokens </interleave>
    | <choice> tokens tokens </group>
    | <choice> <empty/> tokens </group>

token ::=
    <data ...>...</data>
    | <value .../>
    | <choice> token token </choice>
    | <choice> <empty/> token </choice>
    | <difference> token token </difference>

I don't think we can allow <text> in <difference> in <list>, since <text>
can match multiple tokens.  It might be simpler to disallow <text/> in
<list> altogether.

If we allow <not/>, then

<not> p </not>

should be short for

<difference> <data type="string"/> p </difference>

so that <not/> works inside <list>

James