NMTOKEN data type
See the definition in the W3C XML Schema standard.
Where is this type used?
<bookmark> — "element" attribute
<ensemble> — "number" attribute
<link> — "element" attribute
<lyric> — "number" attribute
<lyric-font> — "number" attribute
<lyric-language> — "number" attribute
<supports> — "element" attribute
<supports> — "attribute" attribute