HTML & CSS: The Good Parts

Quirks Mode and Strict Mode

Web browsers use two general types of rendering modes: “quirks” mode and “strict” mode. They are invoked by the presence or absence of certain document type declarations, which are described generally in Chapter 2 and listed on this book’s companion website.

Instead of treating box properties additively, as strict mode does and the CSS 2.1 box model suggests, quirks mode rendering uses stated width and height as the primary reference for computing element dimensions, and subtracts the other box values from those as appropriate. These behaviors are analogous to the behavior of the CSS3 box-sizing property, which has two values: content-box and border-box.

Note

Quirks mode rendering is the only rendering mode available in versions of Internet Explorer prior to IE 6.