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In the example code of Section 7.7, there are various elements with an ID and/or a class name, but they are only referred with names preceded with a hash (#), which is usually used to refer an ID. I guess classes in the example should be replaced with IDs.
Fixed in https://github.com/w3c/webcomponents/commit/541ed9d3a72bd5e4c97f77909d06cc69e04243b8