<button
  class="d-ib p-sm bgc-cool c-warm"
  fxcss-device-tablet-remove="p-sm"
  fxcss-device-tablet-add="p-md"
  fxcss-device-desktop="d-b p-lg bgc-cloudy c-sunshine"
  fxcss-pseudo-class-hover="td-u">
  click me
</button>

doesnt the following look more use friendly?

button({
  class                : 'd-ib p-sm bgc-cool c-warm',
  device_tablet_remove : 'p-sm',
  device_tablet_add    : 'p-md',
  device_desktop       : 'd-b p-lg bgc-cloudy c-sunshine',
  pseudo_class_hover   : 'td-u'
}, [
  'click me'
])

or because now you can use variables and functions, those small combinations of class name “abbreviations” could even be put into meaningful variable names that describe what they actually mean or there could be a function that will be called.

Why would you want to turn a markup language into a programming language?