According to the grammar: http://dev.w3.org/2006/webapi/WebIDL/#idl-grammar, we cannot use static operations which have return types. 

 I think, 

[38]	AttributeOrOperationRest	→	AttributeRest 
                                              | OperationRest 
                                              | ";"

should be

[38]	AttributeOrOperationRest	→	AttributeRest 
                                              | ReturnType OperationRest 
                                              | ";"

For example, suppose that we have "static void classMethod();" declared as "interface member".
According to the grammar: http://dev.w3.org/2006/webapi/WebIDL/#idl-grammar,

[10]	InterfaceMember	→	Const 
                                              | AttributeOrOperationOrIterator

the text matches the rule: InterfaceMember -> AttributeOrOperationOrIterator.

[30]	AttributeOrOperationOrIterator	→	Serializer 
                                              | Qualifier AttributeOrOperationRest 
                                              | Attribute 
                                              | OperationOrIterator

the text matches the rule: AttributeOrOperationOrIterator -> Qualifier AttributeOrOperationRest.

[37]	Qualifier	→	"static" 
                                             | "stringifier"

the text matches the rule: Qualifier -> "static".

[38]	AttributeOrOperationRest	→	AttributeRest 
                                              | OperationRest 
                                              | ";"

the text matches the rule: AttributeOrOperationRest -> OperationRest.

[51]	OperationRest	→	OptionalIdentifier "(" ArgumentList ")" ";"

The OptionalIdentifier matches "void", not "classMethod". So as "(" doesn't match "classMethod", "static classMethod();" is rejected.

Best regards,
Takashi Sakamoto