That which asks, in a system where something else answers. Also one served under an obligation of care.

Instructions written so a machine can carry them out. Also any system where one thing stands for another by agreement.

The Windows shell of objects and verbs — half the street wakes here; its quirks are documented so they bite once.

The surface a system is spoken to in typed text. Also final — the same word for a doorway and for an ending.

Visual Studio Code shortened to its working name — the editor half the house's building happens inside.