Notes from the Google Webmaster Hangout on the 21st of February, 2017.
Iframes Can be Used to Block Content
Iframes can be used to block content from being crawled.
Server Performance and Robots.txt Can Impact HTTPS Migrations
An HTTPS migration might have problems if Google is unable to crawl the site due to server performance issues or files blocked in robots.txt.
AJAX Loaded Hamburger Menus Won't Be Seen by Google
Hamburger menus with content loaded via AJAX probably won’t be seen by Google.
Clean HTTP to HTTPS Migrations Should Take Days
If you do a clean one-to-one redirection to HTTPS, you should see minimal fluctuation of rankings and fairly stable traffic. If you’re seeing an impact on overall rankings and traffic, you should notify Google.
Internal Linking Affects Crawl Frequency
Pages with more internal links are more likely to be crawled more frequently.
Use Redirects to Remove a Separate Mobile Site
Absolute URLs are Required for Sitemaps and Recommended for Internal Links
Relative URLs are fine for internal linking, but Google requires absolute URLs for Sitemaps. Google now recommends using absolute URLs for internal linking to avoid any uncertainty about the preferred protocol.