Layer element

Layers were the core of a method of dynamic HTML programming specific to Netscape 4. Each layer was treated as a separate document object in JavaScript. The content could be included in the same file within the non-standard element (or any other element with the positioning set to "absolute" via CSS) or loaded from a separate file with  or <div src="URL". It could also be generated via JavaScript with the javascript constructor. The content would then be inserted into the layer with layer.document.write.

But in modern browsers, the functionality of layers is provided by using an absolutely-positioned, or, for loading the content from an external file, an.

At the height of the Browser Wars, Netscape 4 and Internet Explorer had significantly different JavaScript implementations. Thus, layers could be used for browser detection. A JavaScript program would very often need to run different blocks of code, depending on the browser. To decide which blocks of code to run, a JavaScript program could test for support for layers, regardless of whether the program involved layers at all. Namely,