using Javascript, is the true ID of a control on a form considered a child node, and if so how do get it.

For example, if I have a variable that I have used to manipulate a control  llike this:
var lbl1= document.getElementById('<%=MainContent.FindControl("Contacts").ClientID %>');If I try to extract the ID of the control later through the variable:var lblID = lbl.getAttribute("id");alert(lblID):I get: "ct100_MainContent_Contacts"Are the "ct100" and "MainContent" child nodes, and if so, what do I have to do to end up with "Contacts" only as an ID for the variable lblID I am trying to create?
 
 
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