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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 layer element (or any other element with the positioning set to "absolute" via CSS) or loaded from a separate file with <layer src="URL"> or <div src="URL">. It could also be generated via JavaScript with the layer = new Layer() 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 div, or, for loading the content from an external file, an IFrame.Irrelevant to the actual ''use'' of layers, when Netscape 4 and Internet Explorer had significantly different JavaScript implementations, a JavaScript program would very often need to run different blocks of code, depending on the browser. To decide which bunches of code to run, a JavaScript program could test for ''support'' for layers, regardless of whether the program involved layers at all. Namely, if( document.layers ) else ==References== * Netscape: Dynamic HTML in Netscape Communicator ((On the Internet Archive )) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Layer element」の詳細全文を読む スポンサード リンク
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