What is event bubbling?
The Server controls such as DataList, Datagrid, Repeater can have another child controls inside them. For example the DataGrid can have combo box inside the datagrid. These child control do not raise there events by themselves, rather they pass the event to the container parent (which can be a datalist ,datagrid, repeater), which passed to the page as "ItemCommand" event. As child control send there events to parent this is known as event bubbling.