[XXE] Displaying attribute differently when present or not?

[Hussein Shafie]

Bill Fenner wrote:
> Many (most) elements in my schema can accept an IDREF attribute named
> "anchor".  I currently have it styled like
> 
> 
> *::attribute(anchor) {
>        attribute-content-left: "[a:";
>        attribute-content-middle: text-field(attribute, anchor, columns,
> 10);
>        attribute-content-right: "] ";
>        show-attribute: when-added;
>        font-size: 80%;
> }
> 
> I would like to have a small button to add an anchor to an element
> when it's missing, something like
> 
> content: command-button(icon, icon(plus), command, "putAttribute",
> parameters, '[id] anchor')
> 
> but I haven't been able to figure out how to use this content if
> there's no anchor attribute but the attribute-* styled items when
> there is an anchor attribute.
> 

What about replacing:

attribute-content-right: "] ";

by:

attribute-content-right: "] "
    command-button(icon, icon(plus),
                   command, "putAttribute",
                   parameters, '[id] anchor');