KNACSS/styl/config/_mixins.styl

// Additionnal "utility" breakpoints aliases
// ex. @include respond-to("medium-up") {...}
breakpoint(bp)
  if bp == 'tiny'
    return '(max-width: %s)' % tiny
  else if bp == 'small'
    return '(max-width: %s)' % small
  else if bp == 'medium'
    return '(max-width: %s)' % medium
  else if bp == 'large'
    return '(max-width: %s)' % large
  else if bp == 'extra-large'
    return '(max-width: %s)' % extra-large
  else if bp == 'tiny-up'
    return '(min-width: %s + 1)' % tiny
  else if bp == 'small-up'
    return '(min-width: %s + 1)' % small
  else if bp == 'medium-up'
    return '(min-width: %s + 1)' % medium
  else if bp == 'large-up'
    return '(min-width: %s + 1)' % large
  else if bp == 'extra-large-up'
    return '(min-width: %s + 1)' % extra-large
  else if bp == 'retina'
    return '(-webkit-min-device-pixel-ratio: 2), (min-resolution: 192dpi), (min-resolution: 2dppx)'

/*
respond-to(value)
  string = breakpoint(value)
  @media screen and string
    {block}
*/