After investigation, this actually violates the spec. The spec says the a named parameter "follows the rules for identifiers defined in Section 4.4.1":

Section 4.4.1 states:

An identifier is a character sequence of unlimited length. The character sequence must begin with a Java identifier start character, and all other characters must be Java identifier part characters. An identifier start character is any character for which the method Character.isJavaIdentifierStart returns true. This includes the underscore (_) character and the dollar sign ($) character. An identifier part character is any character for which the method Character.isJavaIdentifierPart
returns true. The question mark character is reserved for use by the Java Persistence query language.

A number is not a valid "Java identifier start character"