The DevExpress ASP.NET Tree List (ASPxTreeList) allows you to manually validate edited nodes and display errors for invalid fields.
This demo illustrates how to include data validation in your next ASP.NET project. Validation is implemented within the NodeValidating event handler. Invalid values are indicated via error icons. Hovering the mouse over an icon displays a hint along with an error description.
The HtmlRowPrepared event is handled to indicate nodes with invalid data. This event is raised for each node when the corresponding row within the table has been created. In this example, nodes with invalid data are painted in red.