Because we are not compiler writers, we dropped a rarely used feature of Ratfor77 that was not easy for us to implement: Ratfor77 recognizes break 2 which escapes from {{ }}. Breaking out of multiple loops is still possible using the loop naming feature provided by Fortran90.
Changing all the code that generated illustrations for four textbooks (of various ages) also turned up a few more issues: Fortran90 uses the words scale and matmul as intrinsics. Old Fortran77 programs using those words as variable names must be changed. Ratfor77 unwisely allowed variables of implicit (undeclared) types. Ratfor90 includes an implicit none statement in all programs, eliminating a common programming bug.