DO loops

To make nested DO loops more readable you should add the name of the repetitor after the END statement.
Example:

 
  do i = 1 to 4
    do j = 1 to 5
      do k = 1 to 3
        say i j k
      end k
    end j
  end i

Note: As a side effect of this technique the REXX Interpreter can check the nesting of the loops.