I think there is a typo in the sequence conversion algo (http://dev.w3.org/2006/webapi/WebIDL/#es-sequence)
1. Let *length* be the length of the platform array object.
But length is never used - instead, "n" is used in the proceeding steps.
Either change "length" to "n" or replace "n" for "length" in steps 2 and 3.