Documentation for Theme config.json file

I am starting to work on some theme ideas.  Some of this is making sense to me now.  One thing that would be really helpful is  a document explaining all the options available for layout and configuration in the config file.  I am able to copy most of the things I need and they make sense based on testing and comparing the results of my tinkering.  One thing I am wondering is what the size parameter for the separator does, and what the available options are?

{
    "name": "separator",
    "type": "separator",
    "label": "Light",
    "group": "Colors",
    "size": "small"
},