Confused about --tmpfs and --mount in docker run

I am starting out with Docker and I’m confused about the --tmpfs and the --mount command line switches of docker run

I read the official Docker Docs about tmpfs, the man docker-run man page on my system and some tutorials online where they describe the usage of tmpfs.

What I’m not sure is: Why do all the official documentations suggest that --mount is the recommended way to do the mounting of tmpfs filesystems when --mount doesn’t allow you to specify general purpose mount options that the mount command on Linux actually supports.

docker run -it --name test255 --tmpfs /app:rw,noexec,nosuid,async,size=50m,uid=500 ubuntu:14.04

I am not able to find an equivalent command to this docker run command that uses --mount.
From the documentation: --mount only supports:

  • type=tmpfs
  • Common options like: src, dst, ro
  • Type specific options like: tmpfs-size, tmpfs-mode

Why is the --mount command line switch limited or am I not able to find the equivalent command ?