用户单击或输入文本框并在asp.net中验证时的显示范围

How to display a popup with a textbox range when the user tabs into the textbox or clicks it and validate it if the user enters a non-range value in asp.net? Currently i'm using js and css to display a panel using z-index, but no validation. Is there a better way?How to display a popup with a textbox range whe