6.8.1 Labeled statements

labeled-statement:
                identifier : statement
                case constant-expression : statement
                default : statement

1723 A case or default label shall appear only in a switch statement.

1724 Further constraints on such labels are discussed under the switch statement.

1725 Label names shall be unique within a function.

1726 Any statement may be preceded by a prefix that declares an identifier as a label name.

1727 Labels in themselves do not alter the flow of control, which continues unimpeded across them.

1728 Forward references: the goto statement (6.8.6.1), the switch statement (6.8.4.2).