Virtual
=======
Field value generated by a script. Uses the document fields to produce a double value.

.. code-block:: protobuf

    message Field {
        string name = 1;
        FieldType type = 2;
        Script script = 16;
    }

- **name**: Name of the field.
- **type**: Type of the field. Must be set to VIRTUAL.
- **script**: Script to generate the field value.

Example
-------
.. code-block:: json

    {
        "name": "virtual_field",
        "type": "VIRTUAL",
        "script": {
            "lang": "js"
            "source": "field1 + field2"
        }
    }