I wanted to ask here, if google ignores web pages code, how do they evaluate heading tags, semantical tags like bold, italic, etc?
Since there seems to be some "confusion", here's a link a posted quite some time ago in another thread.
Video: Google's Vanessa Fox on Sitemaps and PageRank
The whole video is worth the watch but pay particular attention at the 4:54 mark.
Let's be sure and make a distinction here. "Reading" and "ignoring" are 2 different things. We know they can "read" the meta description and keywords. We also know that they "ignore" them when it comes to actual ranking metrics.
Let's also make the distinction between "broken" code that cannot be read and "invalid" code that can be read. Just because code does not validate doesn't mean it cannot be read and will not render properly.
Furthermore, validated code does not make a site/page more relevant to a query. Validated code does not make a site/page more of an authority on the its subject matter.
I am not advocating since some time now that valid code can have a positive effect for rankings. Valid code is not a ranking factor for Google. But correct and clean code is a requirement of the Google Webmaster Guidelines.
There are HTML elements that are included in the Google rankings factors, like titles, headings, bold and italic tags, alt attributes, etc.
I still recommend to check your code with a validator to make sure that you do not have fatal errors that can choke the crawlers.
One fatal error is BOM, which I asked WilliamC if he thinks too that can choke a crawler, but he was not sure, since he did not test that yet.
For the Web Standards Advocates reading or participating in this thread, I would like to add here that I am a Fanatic Web Standards Advocate, but still I must live with the fact that Google doesn't give a damn about valid code. Trust me.
Look at the page technical statement on my web site. There is my Advocate profile.