CSS3, JavaScript and HTML5 explained

DTD – The Document Type Declaration

A DTD is a Document Type Definition, also know as DOCTYPE. In a document served as text/html, the DOCTYPE informs the browswer how to interpret the content of the page. If the the doctype is not declared, the browser assumes you don't know how to code, and goes into "quirks mode". This post recaps all the DTDs for XHTML and HTML versions for desktop.

http-equiv: the meta attribute explained

The http-equiv attribute is used by servers to gather information about a page using the HTTP header. The meta tag's http-equiv attribute set is similar to a http header. The attribute lets you to send additional information to the browser in the http header. In this post, we discuss the main http-equiv values.