After careful study of IE8's behaviour, I have discovered the Webslices "specification" available here is... well... underspecified. Reminds me of the gooood ol'times of the first browser war. Let me give you two simple examples :

  1. the "spec" says multiple entry-title elements are allowed. Great. But what's the intended browser behaviour if more than one entry-title is specified ? It appears that the browser is supposed to make a whitespace-separated string with all these entry-titles, but that's said nowhere.
  2. far more important, the "spec" lacks information about how the contents of a webslice's popup is created in the case of an in-page webslice (ie not a feed). The spec says:
    • remove everything inside the body element BUT the descendants of the element carrying class hslice that carry themselves class entry-content (and of course the subtree they're the root of)
    • remove all atributes on body
    • preserve stylesheet links and style elements in the head of the document

    But it appears this is not enough... IE8 extracts the CSS styles applied to the hslice element and apply them to the webslice popup's body element... Two possibilities : a) it serializes all computed values that differ from the initial value. b) it climbs up the cascade to find all style rules - including inline - applying to the hslice element and tweak them to make them apply to body.

Item number 2 is not a neglectable issue since it makes IE8's behaviour hard to understand to web authors. From a product point of view, I just don't understand Microsoft here, but you could say it's not the first time, eh ? When you introduce such a new feature in a browser, that's to trigger massive market adoption. Underspecifying the feature to the point web site authors cannot predict the final rendering of their data seems to me, sorry to say, crazy.

I have the gut feeling that what does IE8 here is wrong because it does not help the web author. I have mailed Microsoft about it and got a reply from them. I urged them to reconsider their implementation and implement the current "spec", without copying hslice styles to the webslice's body, in next IE8 beta. Stay tuned.