1. A computer-implemented method for comparing content overlap between a first document and a second document, comprising: using a computer to parse a text of each of the first and second documents into constituent units; using the computer to compute a digest of each of the first and second documents based on the constituent units; using the computer to compare the computed digests; and using the computer to compute a proportion of common contents between the first and second documents and a proportion of distinct contents between the first and second documents based on the comparison.