element-label()Same as element-local-name(), but slightly formatted (e.g. capitalized) in order to make the element local name usable as a title or caption.
element-name()Inserts in generated content the qualified name of the element which is the subject of the CSS rule.
element-local-name()Inserts in generated content the local name of the element which is the subject of the CSS rule.
element-namespace-uri()Inserts in generated content the namespace URI of the element which is the subject of the CSS rule.
DocBook 5 example: the element-label() is "Abstract", the element-name() is "db:abstract", the element-local-name() is "abstract", the element-namespace-uri() is "http://docbook.org/ns/docbook".
abstract:before {
    display: marker; 
    content: element-label();
    font-weight: bold;
    color: #004080;
}