I came across this almost by accident when teaching RDz to a customer recently. He wanted to know if RDz can do "column editing" like another text editor he uses, to which I replied "what's that?". After he described it it sound like the rectangle selection within the tool, which I knew could change a selection of text to upper or lowercase. When we walked through the exercise we found the "Fill Selection" option, which turned out to be exactly what he was looking for. Needless to say this is not something you can do in a plain terminal emulator.
While the video shows this using C++ code, you could just as easily use it to edit a column of declarations in COBOL, or PL/I.