Operator-Pending Mode

The fourth mode you didn't know about.

Keys: d, c, y

Between pressing an operator (d/c/y/...) and pressing the motion, Vim is in operator-pending mode. It's a real mode with its own status ("-- OPERATOR --") and its own mappings.

Operator-pending mode

Vim has four base modes, not three. Between an operator key like d and the motion that completes it, Vim is in operator-pending mode — waiting for a motion or text object.

Tip. Try :onoremap il :<C-u>normal! ^v$<CR> — defines a custom "inner line" text object so dil deletes line content without the leading whitespace or trailing newline.

Watch

#0487 — The # Register
#0488 — The = Register

See also: The Vim Grammar, The Modes