When you have a complex control, likeDataGrid, writing an 
event processing routine for each object (cell, button,row, 
etc.) is quite tediousdifficult.

The controls can bubble up their eventhandlers, allowing 
the main DataGrid event handler to take care of its 
constituents.

Suppose you want a certain ASP.NET function executed on 
MouseOver over a certain button.

in case of some server controlls like 
datagrid,repeter,datalist in that we can add another 
another also like suppose in datagrid we can add check box 
and in that the check event is not raised by itself or 
check box.

check box is in datagrid so that datagrid is parent and 
checkbox is child so that check box send  check event to 
parent that is datagrid .

this pass event from child to parent is called event 
bubbled.then parent pass it to page using itemtemplate

<itemtemplate>
<asp:checkbox id=chk1;oncheck="chked">
</itemtemplate>

in that chked is subroutine and oncheck is event so that 
chked is always public or protected

public sub chked(by val e as event,by val---)

//code
end sub

event bubbling
pass event-from-child-to-parent