Today I needed to be able to insert the current date in emacs and I found the lisp code to do so online, hacked it to give the output I liked and then added it

Today I needed to be able to insert the current date in emacs and I found the lisp code to do so online, hacked it to give the output I liked and then added it to emacs - the program I used to edit the code with? The same running version of emacs that I loaded and tested the code with. I don't know any other editor that can do that.