There's quite a few ways to do this, but here's the easiest. Simply use some JavaScript to set the content of DevEdit when a button is clicked:
<input type="button" onClick="addContent()" value="Add Content">
<script>
function addContent()
{
document.frames[0].frames[0].document.write('<b>test</b>');
document.frames[0].frames[0].document.close();
}
</script>
Of course, you will need to adapt this code for your own use, but it does show the general way to write to the DevEdit component via JavaScript.
