Determines start position of the response.

A Long value.  

object.RangeStart [= value]

The RangeStart Property syntax has these parts:

RangeStart value determines if server should send partial content back to the client, and at which position should partial content start.

wodWebServer will set this value when Delivery is set to Automatic, and client requests partial content. Client will send such request when he wants to resume file transfer, or because he uses download managers that split response in several parts and download them simultaneously.  Together with setting this value, wodWebServer will set RangeEnd, and set StatusCode to 216 (Partial Content response).

You can of course fill up these properties by yourself before sending response, thus forcing wodWebServer to send only part of the file back to the client.