Hey folks, Context: http://krijnhoetmer.nl/irc-logs/whatwg/20110428#l-707
Current browsers disagree about how to handle <div id=x></div><script>var x;</script>. Webkit browsers leave x pointing to the div, whereas IE, Firefox and Opera make x undefined [1]. (There is content that depends on x being undefined, but I don't have any links handy right now.)
My reading of the relevant specs (es5 section 10, WebIDL 4.5.3, HTML 6.2.4) supports the Webkit behavior. To summarize, a property x is defined on the global object pointing to the element before the script block, and when the script block is parsed for variable declarations there's already an x defined and therefore the variable is not initialized to undefined. I therefore propose a spec change is in order.
jgraham summarized the wanted behavior neatly as "id lookup should happen after all other property resolution". Conceptually I think this is like saying that the global environment actually has an outer environment, and this outer environment contains the properties for element lookups (which are currently defined on the global object). Another proposal was to say that properties for element lookup are special and should get overwritten in 10.8.c. Other, better options may also exist.
Open question: Should this be defined directly in HTML, or should WebIDL define it and let HTML annotate Window to enable the necessary exceptional behavior? My initial take was that since both id lookup and window=global is defined in HTML it would fit best there, but it also makes sense to contain finicky DOM-ES interactions to WebIDL.
[1] http://code.google.com/p/chromium/issues/detail?id=80591 -- Magnus Kristiansen "Don't worry; the Universe IS out to get you."
