Sass position mixin, with mixins for setting and resetting coordinates.

position.scss

// Print position coords only.
// https://gist.github.com/brianmcallister/3641867
// 
// $values - Position values. Null values get skipped over.
@mixin pos-coords($values: null null null null) {
  $position-list: top right bottom left;
  $count: 1;
  
  @if length($values) == 1 and $values == 'reset' {
    $values: auto auto auto auto;
  }
  
  @each $value in $values {
    @if $value == 'auto' or $value != null {
      $pos: nth($position-list, $count);
      #{$pos}: $value;
    }
    $count: $count + 1;
  }
}

// Reset position coords mixin.
@mixin reset-coords() {
  @include pos-coords('reset');
}

// Position mixin.
// 
// $type     - Position type.
// $values   - List of position values. Null values get skipped over.
// $z-index  - Optional z-index value.
@mixin position($type: relative, $values: null null null null, $z-index: '') {
  position: $type;
  
  @if $type != 'static' and $type != 'inherit' {
    @include pos-coords($values);
    
    @if $z-index != '' {
      z-index: $z-index;
    }
  }
}