How to implement cascading drop-down editors in dxForm

[DevExpress Support Team: CLONED FROM T456218: dxDataGrid - Cascaded dropdown editors]
I still don't get it.

Let say, I have two dropdowns for "Project" & "Worker"

there are Project A and B. Project A has workers X, Y, Z. Project B has workers K,L,M, N.

When I choose Project A. Only workers X, Y, Z comes out in the dropdown "Worker".

How to implement this using dxForm ?

Here is my code in PHP & Java script :

JavaScript
  $(function ()  
        {  

    var projects = <?= $projects ?>;  
    var workers = <?= $workers ?>;  

$("#form").dxForm({  

    items: [  
        {  
            dataField: "Project",  
            editorType: "dxSelectBox",  
            editorOptions: {  
                items: projects,  
                displayExpr: "name",  
                valueExpr: "id",  
            },  
            validationRules: [{  
                type: "required",  
                message: "Project is required"  
            }]  
        },  
        {  
            dataField: "Worker",  
            editorType: "dxSelectBox",  
            editorOptions: {  
                items: workers,  
                displayExpr: "name",  
                valueExpr: "id",  
            },  
            validationRules: [{  
                type: "required",  
                message: "Worker is required"  
            }]  
        },