For linear undo and undo branches, undo-tree.el is required: https://www.emacswiki.org/emacs/UndoTree https://www.emacswiki.org/emacs/UndoTree Regarding "_",

For linear undo and undo branches, undo-tree.el is required: https://www.emacswiki.org/emacs/UndoTree https://www.emacswiki.org/emacs/UndoTree Regarding "_", you can set up Emacs to treat _ as word constituent by modifying the syntax table. For example: (modify-syntax-entry ?_ "w") For more information, please see: https://www.gnu.org/software/emacs/manual/html_node/elisp/Syntax-Table-Functions.html https://www.gnu.org/software/emacs/manual/html_node/elisp/Sy...