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I include the comments at the bottom of the page.
Is there a way to communicate to Google that they should not use the comments on the page as part of their indexing exercise?
In other words, I want them to use the text of the article to determine where the page ends up in SERPs, but not the text from the comments.
This describes a technical solution. Take care however, whether the search engines might consider what you intend to do as "cloaking with intent to deceive your visitors" or you risk being expelled from their indexes. Only your review of their Webmaster guidelines in the context of your page content and intent can determine whether this is the case.
If you do have a long paragraph of boilerplate on many pages, you probably can help yourself by addressing it in some way. Yes, Google indexes urls, not pages, and an iframe holds a different url. I've also seen the boilerplate text turned into an image to address this challenge.