I read somewhere that HTML5 will not allow document.write() statements.

The following script does use the document.write() statement and it seems to work to create a new window
BUT, I get and error in the error console stating
-----------------------------
Timestamp: 12/9/2012 11:34:22 PM
Warning: XUL box for _moz_generated_content_after element contained an inline #text child, forcing all its children to be wrapped in a block.
Source File: chrome://browser/content/browser.xul
Line: 0
-----------------------------

What is the appropriate statement to replace the document.write() to avoid the error reports?

Code:
<!doctype html5>
<html>
<head>
<title>JS created window</title>
<script type="text/javascript">
function newHTML() {
 var HTMLstring='<HTML>\n';
 HTMLstring+='<HEAD>\n';
 HTMLstring+='<TITLE>New Document</TITLE>\n';
 HTMLstring+='</HEAD>\n';
 HTMLstring+='<BODY>\n';
 HTMLstring+='<P>Hello</P>\n';
 HTMLstring+='</BODY>\n';
 HTMLstring+='</HTML>';
 var newwindow=window.open("", "Window3", "width=320,height=210,scrollbars=yes");

 newwindow.document.write(HTMLstring);  // What is replacement statement for document.write() ???


 newwindow.document.close();
}
</script>
</head>
<body>
<input type="button" value="New Window" onclick="newHTML();">
</body>
</html>