onContext

a property used to define custom context-click (right click) handlers for elements in the DataTable cells

Example

var dtable = webix.ui({
    view:"datatable",
    autoConfig: true,
    data:[
        { text:"<div class='myActive'>click here</div>" }
    ],
    onContext:{
        "myActive":function(event, id, target){
            webix.message("Active area was right-clicked");
        }
    }
});

It's a object property that contains all available handlers.
All the handlers (existing and newly-created) are specified by the related class name.