Put simply, a degree of control is possible over how information travels from a third-party website to Facebook when a page is shared (or liked, etc.). In order to make this possible, information is sent via Open Graph meta tags in the <head> part of the website’s code.What You Need to Know About Open Graph Meta Tags for Total Facebook and Twitter Mastery
If you're designing flexibly, use the viewport meta tag in your <head>.Quick Tip: Don’t Forget the Viewport Meta Tag
You can search for DOCTYPEs all day at w3.org without finding one page that lists them all. And when you do hunt down a DOCTYPE (generally in relation to a particular Recommendation or Working Draft), it’s often one that won’t work on your site.Fix Your Site With the Right DOCTYPE!
