Right now, fenced code blocks can be assigned a class (which is typically used to define the language). But it is impossible to assign more than one class.

You may want to do this, for example, to distinguish input code blocks from output code blocks in a vignette. Right now, if you try to define multiple classes in a markdown fence block, using {.class1 .class2}, the HTML is not parsed correctly as a code block.

For a use case, see: mkdocs/mkdocs#1720

You may want to say: {.python .inputblock} or {.bash .outputblock} to add a second layer of distinguishing code blocks.