HTML_Table::getHeader -- Return the table object for the thead group
Description
     Returns the table object for the thead group
    
     If the usage of the thead, tfoot and tbody groups was not activated via
     the third parameter of the constructor, the grouping will be activated
     automatically when calling this function.
    
Return value
     object - the table object for the thead group
    
Note
This function can not be called
statically.