namespace prefix syntax

Dear all,

Today I was musing about the namespace prefix in RDF. I wish to
extract a prefix for local display, so I am breaking an absolute IRI
into a QName.

My understanding is that a namespace prefix can be
{something-something-something}# or {something-something-something}/
or anything *...?

e.g.
http://www.w3.org/2000/01/rdf-schema#

http://schema.org/

* as defined by https://www.ietf.org/rfc/rfc3986.txt

-Brent