Custom Element MathML test

MathML outside of a custom element: 1012. Seems lke the browser knows how to handle MML already (!!??)

Custom element test: 17616

Another test: 18991234

Question: why is it necessary to put the script referring to "custom-element.js" at the end of the body rather than in the head? This appears to be necessary in order for the innerHTML to be set to the string between the begninning and endiing custom element tags /