In order to ensure robustness and integrity of the annotation data, in cases such as internet connectivity failures or Web browser crashes, the annotation tool is able to recover the annotation status just before the connection failure or the crash: When a user begins an annotation session on a document, the current annotated statues of the document is also maintained on the server automatically, even between saves of the document (on a separate, "shadow" cache of the document).
the server always maintains the last saved state of the document, but also the current state, shared among all annotators currently annotating the document.