When people say “they're engaged,” the phrase “to be married” 'is understood'. [=“they're engaged” is understood to mean “they're engaged to be married”]
We still don't fully 'understand' the causes of the disease. = The causes of the disease are still not fully 'understood'.
He believed it 'was understood' [=believed that everyone had agreed] that he would be paid for the work.
(..) I know Bound was so great ... ... but lots of times, that doesn't happen. Studios aren't that trusting. After spending an hour with them, going through the storyboards ... ... I understood why someone would trust them. So few people understood the original script ... ... they decided to storyboard (..)2001 The Matrix Revisited
(..) How do I get my head around it?" I didn't understand the script. Iunderstood enough to say I liked it ... ... but every time I read it and we got closer, I understood more. I had questions forever and would've constantly tried to change the plot ... ... and they were, "Now Bill, Bill, Bill ... ... (..)2001 The Matrix Revisited