It is not code per se, it is the Google Webmaster Tools verification meta tag as the header code, which is just a line of letters and numbers, without any brackets or anything. And you are supposed to insert it into the Header Code window in the Weebly SEO tools page. Issue is, this line is too long, and, though not visible, it breaks the page by making the header wider than the body on mobile. So, I have been wondering whether this is a known issue and whether any solutions may exist.
For now I have removed this meta tag, so that the site looks normal on mobile, but now wondering whether it would ever show up in search results without it.
