>>I do need to reference it from my code behind. I am setting the value in code behind, and then checking that value in java script. Is this true for input= as opposed to ASP HiddenField types? I tried both, but neither show up in my source. Interestingly in another sample page it works perfect but there isn't a master page involved and thus no Content holder.
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>Any control which is run server side is subject to ID mangling. The next version of ASP.NET is supposed to let you enable/disable name mangling - it annoys a lot of devs. The only way to make sure it doesn't happen is to use something like the asp:Literal control and render in the raw HTML into its Text property.

I put an ID="TrackerMaster" in the init of my master page. Now at least I can assure what the id of both the master page and the content holder are; hopefully they won't change. I didn't realize how much master pages affected things. I have an onload= in the body tag of my sample test and in my real site I have to add that to the master page also. I don't like this idea so working on a different solution. Being in a content holder changes things.
Thanks again
Tim