Manipulating text within the editor is pretty common; e.g. I use shell-mode in Emacs, which is mostly just a normal text buffer (except Return acts differently

Manipulating text within the editor is pretty common; e.g. I use shell-mode in Emacs, which is mostly just a normal text buffer (except Return acts differently when the cursor is over the commandline!); eshell is similar. What I was describing above is manipulating such buffers with external commands (similar to Emacs `shell-command-on-region`)