text: // Math Validation
  // ===============
  
  
  // Valid Columns
  // -------------
  // Check that a column setting is valid.
  @function valid-columns(
    $columns,
    $silent: false
  ) {
    $type: type-of($columns);
    $return: null;
  
    @if $type == number and unitless($columns) {
      $return: $columns;
    } @else if $type == list {
      $fail: null;
      @each $col in $columns {
        @if type-of($col) == number {
          $fail: $fail or if(unitless($col), null, true);
        } @else {
          $fail: true;
        }
      }
      $return: if($fail, $return, $columns);
    }
  
    @if $return != $columns and not($silent) {
      $return: null;
      $warn: '$columns must be a unitless number or list of unitless numbers.';
      @warn $warn + ' Current value [#{$type}]: #{$columns}';
    }
  
    @return $return;
  }
  
  
  // Valid Gutters
  // -------------
  // Check that a gutter setting is valid.
  @function valid-gutters(
    $gutters,
    $silent: false
  ) {
    $type: type-of($gutters);
    $return: null;
  
    @if $type == number and unitless($gutters) {
      $return: $gutters;
    } @else if not($silent) {
      $warn: '$gutters must be a unitless number.';
      @warn $warn + ' Current value [#{$type}]: #{$gutters}';
    }
  
    @return $return;
  }
  