RE: [css-regions] Reworking getNamedFlows()

> "Stylesheet loads block script execution, so if you have a <script> after
> a <link rel="stylesheet" ...>, the page will not finish parsing - and
> DOMContentLoaded will not fire - until the stylesheet is loaded."

Thanks for sharing, I didn't know that. 

Still, my take is that it's bad practice not to have a sane way to get an element by name without creating a static list of something (which will have to be created then GCed for no good reason). This is similar to the reason why we have querySelectorAll(...)[0] vs querySelector(...), or querySelectorAll("#abc")[0] vs getElementById("abc"), and preferred that to document.all["abc"] (even if document.all is a live list, in fact). 

Also, I maintain that (in the case of a browser that delays style computation until it's required) creating a static list force the browser to perform the computation of the style on the whole page, while asking just for the flow you need could allow him to return you a value from the named flow cache directly.

Finally, I don't like the fact it's possible for a NamedFlow object and its listeners/expando to stay in memory while the developer has no access to it: it's an invisible leak and it's probably not a good idea. We should probably setup an event for when a flow changes of state (and switch to NULL) so that the developer can free memory at that point.

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Anyway, to get some sane semantics to getNamedFlows you technically have to return a sequence<NamedFlow>, so I do think we want another method to get a flow by id, but I'm not going to fight for that one.