In the following call, w successfully gets the element, and z does not:

YUI().use('dom','node', function(Y) {

    var w = document.getElementById('hello:1');

    console.log('Hello:1 is: ' + w);

    var z = Y.one('#hello:1');

    console.log('Hello:1 is: ' + z);

});

This is important because Frameworks like MyFaces in JavaServer faces autogenerate the ids, and separate them using semicolons, for example, it is pretty common to see content generated as

<table id='myIdentifier'>
<tr id='myIdentifier:1'>
<td></td>
</tr>
<tr id='myIdentifier:2'>
<td></td>
</tr>
</table>

I tried searching if a colon was an invalid identifier, DOM does not seem to say anything about that
http://www.w3.org/TR/REC-DOM-Level-1/level-one-core.html#ID-637646024

Since some frameworks use it, it would be nice for YUI to be able to retrieve those id, it makes integrating YUI with JavaServer faces difficult.