It seems to be XHML with Dublin Core metadata, a set of metadata field standards.
In HTML, Dublin Core info is used in meta and link elements only, and I can not find any instance where the data is validly used in a span element. Also, the content attribute is not valid in HTML.
See Expressing Dublin Core in HTML/XHMTL meta and link elements.
The case is different with XHTML: As @tomlog points out in his comment, the notation you quote is used in this example on Wikipedia.
Given an empty instance of an element whose content model is not EMPTY (for example, an empty title or paragraph) do not use the minimized form (e.g. use <p> </p> and not <p />).
Best Answer
It seems to be XHML with Dublin Core metadata, a set of metadata field standards.
In HTML, Dublin Core info is used in
metaandlinkelements only, and I can not find any instance where the data is validly used in a span element. Also, thecontentattribute is not valid in HTML. See Expressing Dublin Core in HTML/XHMTL meta and link elements.The case is different with XHTML: As @tomlog points out in his comment, the notation you quote is used in this example on Wikipedia.