Basic syntax
The basic syntax of the <layer> tag can't be simpler (as if any tag in HTML is complicated!):
<layer>Text inside layer</layer>
The <layer> tag is a content tag, which means you can add into it content (like <table>). Go ahead, try inserting the above code onto your page...you'll notice that the text inside the layer floats above other text, and overlaps them. Imagine a layer as a sheet of paper that resides on top of the rest of the page, and does not take up space within the flow of the document.
Layer attributes
A layer by itself can't be more boring, not to mention useless. Fortunately, there's more to it. Layers support attributes that allow you to position it using the x,y coordinates-system, give it a background, clip it (make only certain area of the layer visible), hide it from view, and so on. I've listed the most important layer attributes below:
|
id |
The name of the layer, used to identify it in your script |
|
left |
The position of the layer in relationship to the x coordinates |
|
top |
The position of the layer in relationship to the y coordinates |
|
width |
The width of the layer, in px or % |
|
height |
The height of the layer, in px or % |
|
bgColor |
The background color of the layer |
|
background |
The background image of the layer |
|
src |
The external html document contained inside the layer |
Mix and match different attributes any way you like. Here's a sample layer that uses some of the above attributes:
|
<layer id="mylayer" width=100px height=70px
bgColor="yellow"><h3>A layer</h3></layer>
A layer |
Notice I didn't specify the left and top attributes. When you don't, the layer is positioned where you defined it.
-Scripting layers
Here's one of the most important thing to learn about layers- how to script them. After all, its the scripts that make layers come alive. To access a layer, you need to use the following syntax:
document.layername
Accessing the layer is just the first step. Once you've accessed a layer, you can then go on and manipulate one of the layer's attributes to produce dynamic effects. I'll show a simple example where a layer's background color interchanges between red and blue:
Here's the source code I used:
<layer id="test" width=80px height=80px></layer>
<script language="JavaScript1.2">
//variable that helps alternate between red and blue var thecolor=true
//Apply a bgColor of blue as the initial layer color
document.test1.bgColor="blue" function changecol(){ //if thecolor=true
if (thecolor) document.test.bgColor="blue" else
document.test.bgColor="red"
//set thecolor to the opposite of its current state thecolor=!thecolor
setTimeout("changecol()",1000) } changecol() </script>
All of the layers' attributes are read/write, so be sure to experiment with each of them!