Yesterday at PubCon, Gary Illyes from Google said something that got attention by the folks in the audience. He said that where you place your content on your page can impact your rankings. He said this in relation to how you might see ranking changes with the mobile first index if your mobile pages have content in different places than the desktop version.
Here are the tweets from what he said:
Now, we've said this for a long time that now CSS positioning no longer is as valuable as it was. Moving content to the top of your page in the code, even though it is on the footer, might not work as well. Well, maybe for this featured snippet it worked but generally, maybe not so much. Google renders the way your page looks and based on that it knows the location of your content placed on your page.If you reorder your page from desktop to mobile, your ranking will be different because your focal point would have changed. @methode #pubconâ" Jesse McDonald (@jesseseogeek) February 21, 2018
So Google is able to see what content is at the top and what is at the bottom, regardless of where the content is in your HTML.
So this is probably not new to some SEOs but clearly this is being reinforced now by Google.
Forum discussion at Twitter.