How are interface and flush interface different from monitor or unmonitor

[jkilpatr]

So the babeld man page seems to imply that monitor and unmonitor are the config commands to add and remove interfaces https://www.irif.fr/~jch/software/babel/babeld.html

But as we see here althea-net/rita@ccd34fa

unmonitor doesn't work and we have to use flush iface instead, what's the real difference?