ComboBox in Ajax ControlToolkit

I have tried the combobox example here

http://www.asp.net/AjaxLibrary/AjaxControlToolkitSampleSite/ComboBox/ComboBox.aspx

but I can't edit anything in the combobox. I have read the documentation and as far as I understand I do write but still it's not possible to write anything

in it.

Can somebody give me perhaps a short example what settings I need to have to edit in a combobox

//Tony