Ajax Drop down with editable text box

Hi,

Ima using Ajax combo box with editable text box and i need to do some validation on new item entered(ex it shuld be greater than 10 like tat) .can any one tell how to do?

<ajax:ComboBoxItemInsertLocation="OrdinalText"ID="ddlaccount"DropDownStyle=DropDownAutoCompleteMode=SuggestAppendWidth="145px" runat="server"AutoPostBack="true" TabIndex="2"></ajax:ComboBox>