I am looking for a way to collect code parts between two strings (i.e. BEGIN: and :END) stored in the main buffer (primary_buffer) display them in the separate buffer (secondary_buffer), where I could define different major mode, with possibility to change these parts interactively (changes made in the secondary_buffer also are made in the primary_buffer and vice versa). Maybe there is something already made for this purpose. If not from where I should start? I am a novice in Emacs.