FullImage field in order streaming API

[jptrader]

I came across an undocumented field in the order changes in the order streaming API. This is the "FullImage" field that can be found in the "orc" array, see this example:

{"op":"ocm","id":0,"initialClk":"xxxxxx","clk":"AAAAAAAAAAAAAA==","conflateMs":0,"heartbeatMs":5000,"pt":1473854320288,"ct":"SUB_IMAGE","oc":[{"id":"1.126856000","orc":[{"fullImage":true,"id":....

What is the significance of this field? I can see no mention of it in the documentation. The field is present in some orderChanges, not present in others.