SP2010 JavaScript - set_item property and list of values

I have a custom form where the interface is set via JavaScript in a Content Editor web part.

Several of the fields are combo boxes.  For example, the Manager field:

var objEEList = objWeb.get_lists().getByTitle("Entry Exit");
var objItemInfo = new SP.ListItemCreationInformation();
var objListItem = objEEList.addItem(objItemInfo);
objListItem.set_item("ManagerId", DDManager.options[DDManager.selectedIndex].value);

The ManagerId column in this table ("Entry Exit") is type 'Single line of text'.

My question concerns the second parameter in the .set_item function, "DDManager.options[DDManager.selectedIndex].value".  What does this refer to?  Where is it pulling the values from?  This syntax is consistent for the other few columns that are combo boxes.

Thanks,

- Bruce

- Bruce