That is exactly the approach taken in XSPF: http://www.xspf.org/xspf-v1.html#rfc.section.4.1.1.2.14.1.1.1.2 http://www.xspf.org/xspf-v1.html#rfc.section.4.1.1.2

That is exactly the approach taken in XSPF: http://www.xspf.org/xspf-v1.html#rfc.section.4.1.1.2.14.1.1.1.2 http://www.xspf.org/xspf-v1.html#rfc.section.4.1.1.2.14.1.1.... Notice that the cardinality is "zero or more."