I'd like to say technically yes, since really what gets rendered is technically always browser dependent. Most browsers try to keep to the specifications as best they can and as far as I know there is nothing in the css specifications against it. I'm only going to vouch for the actual html,css,javascript code that gets sent to the browser before any other interpretter steps in.
However I also say no since every browser I typically test on doesn't actually let you. If you need to see for yourself save the following as a .html file and open it up in the major browsers. In all browsers I tested on the javascript function will not match to an element. However, remove either "hunkojunk" from the id tag and all works fine. Sample Code
<html>
<head>
</head>
<body>
<p id="hunkojunk1 hunkojunk2"></p>
<script type="text/javascript">
document.getElementById('hunkojunk2').innerHTML = "JUNK JUNK JUNK JUNK JUNK JUNK";
</script>
</body>
</html>