Associate an icon image with command

[Kohei Yoshida]

Could someone refresh me on how to associate an icon image with an
internal command (e.g. ".uno:DoFoo")?

I did it once, many years ago, but I can't remember the process. There
was something very non-obvious about this, like you have to set some
flag to 1 to enable that image or something like that.  Also that the
command name is loosely associated with the name of the image file
etc.

Thanks,

Kohei