code: function (type, breakpoint, val) {
          if (!!val === false) {
              return false
          }
  
          var className = type;
  
          if (breakpoint) {
              className += "-" + (breakpoint.replace(type, '')); // -md ?
          }
  
          if (type === 'col' && (val === '' || val === true)) {
              return className.toLowerCase() // .col-md
          }
  
          return (className + "-" + val).toLowerCase()
      }
docs: Creates Bootstrap specific breakpoint classes.