9. A non-transitory computer-readable storage medium having executable computer program instructions embodied therein, the instructions comprising: instructions for receiving, from a first client device, a notification of a change to a content item stored on the first client device, the notification of the change comprising an indication of a first semantic location of the change within the content item and an indication of a first version of the content item at a time of the change; instructions for determining, based on the indication of the first version of the content item, whether a second client device has made a second change to the content item with respect to the first version of the content item; instructions for providing a notification of change rejection to the first client device responsive to determining that the second client device has made the second change, the notification of change rejection comprising an indication of a second semantic location of the second change within the content item, the indication of the second semantic location having been provided by the second client device; instructions for receiving a request from the second client device to receive changes to the content item; instructions for registering the second client device to receive changes to the content item; instructions for receiving from the first client device a notification of a third change resulting from the first client device combining the change and the second change, the notification of the third change comprising an indication of a third semantic location of the third change within the content item; and instructions for, responsive to receiving the notification of the third change, providing a notification of the third change to the second client device.
12. The non-transitory computer-readable storage medium of claim 9 , wherein the indications of the first and second semantic location are specified in terms of an indicator of a record within the content item and an indicator of a field within the record.