I just started to work on the help file for StartCommand's portBindings field.
I found the snytax quite confusing because it is different form the syntax of the docker program. In particular, it reverses argument order:
|docker run -p
||Port bindings field
I suggest to use the Docker CLI syntax here, optionally allowing white space instead of a colon as the delimiter between host and container part of each binding definition.
@vjuranek If you agree, I'd be happy to create a PR implementing that.