Where is the `cty` tag registered

[OR13]

https://github.com/veraison/go-cose/blob/ebba05d25c1dc9a5eed3acf25446b7931291e1f4/headers_test.go#L31

Not showing up in this list: https://www.iana.org/assignments/cose/cose.xhtml

What is its integer mapping?

[qmuntal]

cty is an abbreviation for content type, which refers to a COSE header parameter with label 3.

[OR13]