HTML and CSS Reference
Throughout this topic I'll be discussing various properties and how
they behave according to the W3C and thus in Standards Mode.
Almost Standards Mode was developed as a compromise between
the stricter Standards Mode rendering and the implications of <img>
being an inline element. Under Standards Mode, images had a space
underneath them just as text does—the space for text is reserved for
the descender of characters such as g and q . This caused images sliced
up and then recombined inside a table-based layout to suddenly not
match up as they were intended. Almost Standards Mode is identical
to Standards Mode with the sole exception that it closes up the space
Quirks Mode is a legacy rendering mode in some browsers that allows
the browser to behave like a previous version of that browser. Quirks
Mode, by definition, works differently in various web browsers and does
not fully follow any CSS specification. It is useful mainly for letting old
sites live on without the need for maintenance and for allowing code
built to work only in a specific browser to continue working.
Building new sites under Quirks Mode is difficult because of the
behavior differences between browsers and the different ways they
diverge from the CSS2 and CSS3 specifications. Stick with Standards Mode if
you're building new sites, and forget that anything else exists.
At the time that browser vendors were implementing rendering modes,
the Web was largely a mess of invalid tag-soup HTML4, browser-targeted