new keyword 'extension' really necessary?

[Gernot Neppert]

Hi Maurizio,

I do not have compiler writing skils, so I'm curious why the keyword 
'extension' should be nessesary to introduce defender methods.
A defender method declaration without the prefix 'extension' looks quite 
distinguishable to me. Example:

interface List<E>
{
    void sort(Comparator<? super E> comp) default Collections.sort(List<E>);
}

So, why the new keyword?

(An answer such as 'This is necessary to disambiguate the grammar' would 
suffice...)