entity-singleton = authority-singleton / class-singleton
authority-singleton = person-singleton / legal-singleton / general-singleton
class-singleton = unreserved-class / reserved-class
person-singleton = "=" C-I ( xdi-name / xref / xdi-scheme )
legal-singleton = "+" C-I ( xdi-name / xref / xdi-scheme )
general-singleton = "*" C-I ( xdi-name / xref / xdi-scheme )
unreserved-class = "#" C-I ( xdi-name / xref / xdi-scheme )
reserved-class = "$" C-I xdi-name
entity-collection = authority-collection / class-collection
authority-collection = person-collection / legal-collection / general-collection
class-collection = reserved-collection / unreserved-collection
person-collection = COLL "=" COLR
legal-collection = COLL "+" COLR
general-collection = COLL "*" COLR
reserved-collection = COLL reserved-class COLR
unreserved-collection= COLL unreserved-class COLR
entity-member = member
member = ordered-member / unordered-member
ordered-member = "@" C-I ( ( %x31-39 DIGIT ) / "0" )
unordered-member = "!" C-I ( xdi-name / xref / xdi-scheme )
