jQuery自动完成：确定输入的文本是否不匹配

I've got jQuery Autocomplete (UI 1.6rc2) up and running fine and when the user picks an item, it updates a hidden form value with the associated ID. How do I set the hidden form value to '0' when the text entered does not match a result from the autocomplete list? In this case, I'll be creating a new entry.I've got jQuery Autocomplete (UI 1.6rc2) up and