The OVERLAY function description in the "Open Object Rexx Reference" (Section 8.4.42 on page 322 of the Version 3.1.0 Edition, dated August 15, 2006) contains a syntax error. The second sentence after the OVERLAY function's syntax diagram reads:
"The overlay must extend beyond the end of the original target string."
This wording is inconsistent with the actual operation of the function (as well as the way the function is intuitively expected to work).
According to the description given in the z/OS TSO/E REXX Reference (cf. http://publibfp.boulder.ibm.com/cgi-bin/bookmgr/BOOKS/ikj4a370/4.3.43?DT=20060626210253), this sentence should read:
"The overlay may extend beyond the end of the original target string."
No response is necessary, but if you insist, I can be reached at: firstname.lastname@example.org (please let me know if my understanding is incorrect).