Andy,
Check this demo:
The html source of the pop up is as following:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>Insert Text</title>
</head>
<body bgcolor="buttonface">
<div align="center" style="padding:8px">
<textarea rows="6" cols="40" id="ta">Type content here</textarea>
<br>
<button onclick="button_click()">Insert It</button>
<button onclick="window.close()" ID="Button1">Close</button>
</div>
</body>
<script>
function button_click()
{
var editor=window.dialogArguments;
editor.ExecCommand("PasteHTML",false,ta.value);
}
</script>
</html>
Hope it helps.
Let me know if you have any further questions.
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