-+dit(bf(--detect-renamed)) This option tells rsync to scan the receiving
-+side for files that have been renamed, and to use any that are found as
-+alternate basis files to help speed up the transfer.
++dit(bf(--detect-renamed)) With this option, for each new source file
++(call it em(src/S)), rsync looks for a file em(dest/D) anywhere in the
++destination that passes the quick check with em(src/S). If such a em(dest/D)
++is found, rsync uses it as an alternate basis for transferring em(S). The
++idea is that if em(src/S) was renamed from em(src/D) (as opposed to em(src/S)
++passing the quick check with em(dest/D) by coincidence), the delta-transfer
++algorithm will find that all the data matches between em(src/S) and em(dest/D),
++and the transfer will be really fast.
++