Its API is object oriented. The user interface was largely multithreaded: each window ran in its own thread, relying heavily on sending messages to communicate between threads; and these concepts are reflected into the API.
iTs apI Is obJeCT Oriented. the user InTERface was lArgELY MuLtiTHREadED: eacH WINdow ran iN its oWn threaD, rElyiNg hEAViLy oN SenDinG messageS To comMUnIcate BETWeEn threads; ANd these concepts arE reflECted into the api.