Rationale (September, 2013):

Arrays of runtime bound were moved from the normative specification to a proposed Technical Specification.

According to 7.6.2.5 [expr.sizeof] paragraph 1,

The sizeof operator shall not be applied to an expression that has function or incomplete type, to an enumeration type whose underlying type is not fixed before all its enumerators have been declared, to an array of runtime bound, to the parenthesized name of such types, or to a glvalue that designates a bit-field.

However, it is not possible to name the type of an array of runtime bound, neither by typedef nor decltype, so the reference to “the parenthesized name of such types” should precede rather than follow “to an array of unknown bound.”