21. The method of claim 1 , wherein the identifying of the set of matches for which a total cost is minimal comprises: inputting a matrix with cost values which are a function of a measure of similarity for the content of pairs of leaves, the pairs of leaves each including a leaf of a source document and a leaf of a target document, each of the leaves including document content; computing a minimum edit distance for the matrix based on the input cost values, whereby each leaf from the source document is aligned with a leaf of the target document or with no leaf of the target document and each leaf from the target document is aligned with a leaf of the source document or with no leaf of the source document; and from the matrix alignments, identifying candidate matches in which a leaf of at least one of the source and target documents matches a combination of leaves of the other of the source and target documents; refining the candidate matches to identify the probable matches; and the output alignment of the leaves of the first document with the leaves of the second document includes matches of at least some of the leaves of the first document with at least some of the leaves of the second document.
21. The method of claim 1 , wherein the identifying of the set of matches for which a total cost is minimal comprises: inputting a matrix with cost values which are a function of a measure of similarity for the content of pairs of leaves, the pairs of leaves each including a leaf of a source document and a leaf of a target document, each of the leaves including document content; computing a minimum edit distance for the matrix based on the input cost values, whereby each leaf from the source document is aligned with a leaf of the target document or with no leaf of the target document and each leaf from the target document is aligned with a leaf of the source document or with no leaf of the source document; and from the matrix alignments, identifying candidate matches in which a leaf of at least one of the source and target documents matches a combination of leaves of the other of the source and target documents; refining the candidate matches to identify the probable matches; and the output alignment of the leaves of the first document with the leaves of the second document includes matches of at least some of the leaves of the first document with at least some of the leaves of the second document. 22. The method of claim 21 , wherein a maximum cost value is assigned to unmatched pairs in which a target leaf has no corresponding source leaf or a source leaf has no corresponding target leaf.