9. The method of claim 1 , comprising determining whether a time stamp of a change record for the first document instance of the collaborative document and a time stamp of a change record for the second document instance of the collaborative document are both within a synchronization interval when the change records have matching constructs, and annotating the change records as conflict records.
1. A method implemented in computer hardware, comprising: processing a collaborative document having a presentation surface with multiple constructs; rendering a first document instance of the collaborative document; receiving a document update list comprising a set of change records for a second document instance of the collaborative document, each change record comprising information for a modification made to a construct of the second document instance; determining that a time stamp of an undo record and a time stamp of a change record are both within a synchronization interval when the undo record and the change record have matching constructs, annotating the undo record as a conflict record, and resolving the conflict record using a set of construct-based conflict rules; modifying properties of one or more constructs for the first document instance based on the change records to form a merged document instance of the collaborative document; managing a local undo stack for the first document instance, the local undo stack comprising a set of undo records each storing information to undo a modification made to a construct of the first document instance; and preserving one or more of the undo records of the local undo stack after formation of the merged document instance based on one or more of the change records.