Layer Mask in Illustrator

<body> <center>Sorry you do not have frames enabled. Here is the link of the tutorial:<br> <a href="http://www.bittbox.com/illustrator/improve-your-illustrator-workflow-with-layer-masking/">http://www.bittbox.com/illustrator/improve-your-illustrator-workflow-with-layer-masking/</a></center> </body>