For Todo mode commands to function properly, it is essential to maintain the correct format at all three levels of organization—item, category, and file. Todo mode tries to minimize the risk of format corruption by hiding certain parts of the format from the user, making the buffer read-only and suppressing the self-insertion keys. Consequently, it is normally impossible to make changes to your todo files without explicitly invoking Todo mode commands.
A beneficial side effect of this restrictiveness is that you can invoke almost all Todo commands by typing ordinary printing characters, either singly or in specified sequences, without using modifier keys, except for the shift key for capitalization and the raw prefix argument C-u; numeric prefix arguments can be entered just by typing a number key.
The predefined key bindings in Todo are more or less mnemonic. As a rule, key sequences beginning with C (capital ‘C’, not the control key) are bound to commands applying to categories, sequences beginning with F apply to (non-archive) file-level commands, and those beginning with A apply to archives (a special type of Todo file; Todo Archive Mode). Todo commands applying to items, which constitute the majority, are bound to lower case key sequences.