property(property_qualified_name)

Inserts in generated content the value of a (application-level) property of the element which is the subject of the CSS rule.

Example: topmost included elements have a {http://www.xmlmind.com/xmleditor/namespace/property}inclusion property. Make these properties visible in the styled view.

@namespace prop "http://www.xmlmind.com/xmleditor/namespace/property";

*:property(prop|inclusion):before {
    content: icon(left-half-disc) 
             "inclusion=" property(prop|inclusion) 
             icon(right-half-disc);
}

See also Section 14, “:property() extension pseudo class”.