A combobox is like a text <input> field (ie, you can input any value you want), but it also has a list of suggested values that you can choose from. The drop down list is filtered by the data you have already typed in.
ComboBox #1: inlined data, autocomplete=false:
ComboBox #2: dataUrl, autocomplete=true:
ComboBox #3: dataUrl, autocomplete=false:
this is some text below the combo boxes. It shouldn't get pushed out of the way when search results get returned. also: adding a simple combo box to test IE bleed through problem: