When discussing this standard we have to recognize that not all
browsers actually have a "main thread". Time will tell if more or less
browsers of the future will have multi-threaded architectures, but the
trend has been for more I think.
Any aspects of the spec that asserts or assumes a "main thread" is
questionable.
Yes they do -- we're talking about the main thread from the point of
view of javascript, which is not necessarily the UI thread.
The important thing is that with the current model is that JS on any
thread may be blocked by js executing in a worker, which leads to a
page (in effect) locking up -- the UI may still be functional but that
particular page will have hung.
--Oliver
