How to modify headlines programmatically

Do you know about the Emacs Lisp function split-line? | back-to-indentation, split-line

How to display the documentation of the symbol at point Emacs Lisp? | symbol-at-point

How to write buffer region into a file in Emacs Lisp? | write-region, make-directory

How to select a word in a list with minibuffer completion in Emacs Lisp? | completing-read

How to loop over the window list of the selected frame in Emacs Lisp? | window-list, window-buffer

How to save and restore the selected window in Emacs Lisp? | save-selected-window

How to stop displaying calls to message in Emacs Lisp? | inhibit-message, sleep-for

How to move the point around in buffers in Emacs Lisp? | point, point-min, point-max, goto-char

How to start a shell in a window below in Emacs Lisp? | select-window, split-window-below, shell

How to copy the current line below in Emacs Lisp? | buffer-substring, save-excursion, forward-line

How to run a unix utility on file at point in dired in Emacs Lisp? | dired-file-name-at-point

How to swap elements in vectors in Emacs Lisp? | cl-rotatef