[stmt.label]

{o p t identifier : attribute-specifier-seq {o p t case constant-expression : attribute-specifier-seq {o p t default :}_{o p t default :}}_{o p t case constant-expression : attribute-specifier-seq {o p t default :}_{o p t default :}}}_{o p t identifier : attribute-specifier-seq {o p t case constant-expression : attribute-specifier-seq {o p t default :}_{o p t default :}}_{o p t case constant-expression : attribute-specifier-seq {o p t default :}_{o p t default :}}}

The optional attribute-specifier-seq appertains to the label.

The only use of a label with an identifier is as the target of a goto.

No two labels in a function shall have the same identifier.

A label can be used in a goto statement before its introduction.

A labeled-statement whose label is a case or default label shall be enclosed by ([stmt.pre]) a switch statement ([stmt.switch]).

A control-flow-limited statement is a statement S for which:

(3.1)
a case or default label appearing within S shall be associated with a switch statement ([stmt.switch]) within S, and
(3.2)
a label declared in S shall only be referred to by a statement ([stmt.goto]) in S.

An identifier label shall not be enclosed by an expansion-statement ([stmt.expand]).