Take a look at rxmath.pdf.  It has examples of requires. 
On Jul 15, 2013, at 6:36 PM, J. Leslie Turriff wrote:

:-) When I search my copy of  Open Object Rexx™
Unix Extensions Reference (Version 4.1.0 Edition, December 2010) 
for "Introduction" I get "No matches found for 'Introduction'."
When I search for "::requires" I get "No matches found for '::requires'."

Leslie