Include specific attribute or child-element text in breadcrumb rendering

Within the author it displays a breadcrumb, and I know you can modify its display to either some other static text or localisation, but I'm wondering if it's possible to dynamically show an attribute, or execute some other context-specific xpath dynamically.

As a test I can change the breadcrumb using the localisation editor variable ${i18n()}.

_{cc_config.xml}

<elementRenderings platform="webapp">
    <render element="num" as="${i18n(test)}" annotation="${i18n(test)}"/>

_{translation-cc.xml}

<key value="test">
    <comment></comment>
    <val lang="en_US">Year</val>

"Year" is actually a num element.

However, trying any other variable, even 'more static' ones like ${cf} or ${tp} simply render the variable text literally, instead of evaluating it.

_{cc_config.xml}

<elementRenderings platform="webapp">
    <render element="paragraph" as="${xpath_eval(./@eId)}" annotation="${xpath_eval(./@eId)}"/>
    <render element="p" as="${tp}" annotation="${tp}"/>

(paragraphs do have an eId attribute)

As you can see, I tried using annotation; but these tooltips also simply display the variable literally.
I also fiddled and tried a bunch of xpath stuff, like @eId/.@eId//@eId, but I think there's some restriction in using the Content Completion Configuration File with respect to editor variables.

So is the thinking right but I am doing something wrong, or is it not the right way but there is some other way to affect the breadcrumb? Maybe with the schema?

Solution

The element display names in cc_config.xml file do not support most of the editor variables. Most of them, like ${cf} (current file) and ${tp} (total number of pages) don't make sense to be used when rendering the name of an element.

The xpath_eval would make sense - the display name of an element may depend on its attributes (e.g. the @id attribute), it's index in the document (e.g. 'Section 3'), etc. We have a feature request registered for this case and I added your vote to it.

As a partial workaround you can use a JS API to compute the display name of the element based on the element original name and its attributes:

goog.events.listen(workspace, sync.api.Workspace.EventType.BEFORE_EDITOR_LOADED, function(e) {
  e.options.elementNameEnhancer = function(elemName, attrs) {
    var displayString = elemName;
    var attr = attrs['id'];
    if (attr) {
      displayString += ' (#' + attr.attributeValue + ')';
    }
    return displayString;
  };
});