Tonearm - 6:22 pm on Feb 28, 2010 (gmt 0)
For example, can they be placed on a div that surrounds some anchor text and some non-anchor text?
No. That's what HTML Elements are for. Microformats take the Elements and allow you to refine them further. Your root class can be assigned to the <div> that surrounds that content. And then you assign additional properties to those items within the root class.
I'm not sure if we're talking about the same thing. I'm wondering about this since part of the category is anchor text and part is not:
<a href="page.html">Red</a> Widgets
Does anyone have any ideas on how Google might use this data?
I'm going to reference the links above again. Google states how they are currently using this data.
I should have been more specific, I meant how will they use it in the future. They do state how they're using it now, and I think we can agree that the best way to apply hproduct considering the current state of Rich Snippets is to use it only on the main product appearing on each product detail page. That seems in-line with the way Google uses the data now, as demonstrated by the tool you linked to:
If I "preview" a page with that tool that has more than one hproduct definition, Google only shows the main product.
The question for me is, how will Google use hproduct in the future? It seems they want to break up a site's data into well-defined portions for display on their own site. I don't see how defining hproduct on more than the main product on each product detail page will help that along.
Considering how rich snippets work, isn't it better to send a clear signal regarding which product a page is about, if any?
You can send clear signals from anywhere. If the content is wrapped in the proper semantic containers, the signal is there. Whether it be a partial signal or full signal, it is all part of the process.
This seems similar to the question of whether or not to use alt image text on every product image. For example, on a product detail page, should alt image text be used on the photos of items that are displayed for cross-selling purposes? That alt image text doesn't speak about the main theme of the page, which is the detailed product. I think some would say include it, and some would say don't, but I bet you would include it. :) You could be right too, it's just an example of defining pages vs. defining page elements.
Shouldn't we be sure the search engine signals we include on a page define the page in accordance with the search engines' usage of those signals?