DOCUMENT MODES
Internet Explorer 5.5 introduced the concept of document modes through the use of doctype switching. The first two document modes were quirks mode, which made Internet Explorer behave as if it were version 5 (with several nonstandard features) and standards mode, which made Internet Explorer behave in a more standards-compliant way. Though the primary difference between these two modes is related to the rendering of content with regard to CSS, there are also several side effects related to JavaScript. These side effects are discussed throughout the book.
Since Internet Explorer first introduced the concept of document modes, other browsers have followed suit. As this adoption happened, a third mode called almost standards mode arose. That mode has a lot of the features of standards mode but isn't as strict. The main difference is in the treatment of spacing around images (most noticeable when images are used in tables).
Quirks mode is achieved in all browsers by omitting...