Is "order" attribute of feConvolveMatrix required or not?

http://www.w3.org/TR/SVG/filters.html#feConvolveMatrix says

 order %NumberOptional
<http://www.w3.org/TR/SVG/types.html#DataTypeNumberOptionalNumber>Number.datatype
<http://www.w3.org/TR/SVG/types.html#DataTypeNumber>; #REQUIRED


But it also says
> If the attribute is not specified, the effect is as if a value of "3" were
specified.

Is it required or not? Currently Gecko treats it as required.

Rob
-- 
"He was pierced for our transgressions, he was crushed for our iniquities;
the punishment that brought us peace was upon him, and by his wounds we are
healed. We all, like sheep, have gone astray, each of us has turned to his
own way; and the LORD has laid on him the iniquity of us all." [Isaiah
53:5-6]