Yaml: options per boxstyle

[ute]

(thinking loudly) when (if) making an interface for other custom block styles, it would be logical to put options that affect the rendering/style, like collapse, as a subkey under the respective boxstyle key. This would however make the boxstyle key compulsory, and give endless cascades… Default is foldbox

groups:
   Theorem:
       boxstyle: {foldbox.simple, collapse=true}

???