12. The method of claim 10 wherein each document tree structure includes a plurality of subtree structures, and wherein aligning the document tree structures comprises: aligning nodes in the subtree structures to obtain subtree alignments; and aligning the plurality of subtree structures, to align the document tree structures, based on the subtree alignments.
12. The method of claim 10 wherein each document tree structure includes a plurality of subtree structures, and wherein aligning the document tree structures comprises: aligning nodes in the subtree structures to obtain subtree alignments; and aligning the plurality of subtree structures, to align the document tree structures, based on the subtree alignments. 13. The method of claim 12 and further comprising: iteratively repeating the steps of aligning nodes in the subtree structures to obtain subtree alignments and aligning the plurality of subtrees structures based on the subtree alignments.