//**
   Example 1:
   a.twitter
     +sprite-img("icons-32.png", 1)
   a.facebook
     +sprite-img("icons-32png", 2)
   ...
   Example 2:
   a
     +sprite-background("icons-32.png")
     a.twitter
       +sprite-column(1)
     a.facebook
       +sprite-row(2)
     ...
  
 !sprite_default_size  ||= 32px
 !sprite_default_margin ||= 0px
 !sprite_image_default_width ||= !sprite_default_size
 !sprite_image_default_height ||= !sprite_default_size
  
  
 // Sets all the rules for a sprite from a given sprite image to show just one of the sprites.
 // To reduce duplication use a sprite-bg mixin for common properties and a sprite-select mixin for positioning.
 =sprite-img(!img, !col, !row = 1, !width = !sprite_image_default_width, !height = !sprite_image_default_height, !margin = !sprite_default_margin)
   +sprite-background(!img, !width, !height)
   +sprite-position(!col, !row, !width, !height, !margin)
  
 // Sets rules common for all sprites, assumes you want a square, but allows a rectangular region.
 =sprite-background(!img, !width = !sprite_default_size, !height = !width)
   +sprite-background-rectangle(!img, !width, !height)
  
 // Sets rules common for all sprites, assumes a rectangular region.
 =sprite-background-rectangle(!img, !width = !sprite_image_default_width, !height = !sprite_image_default_height)
   :background= image_url(!img) "no-repeat"
   :width= !width
   :height= !height
   :overflow hidden
  
 // Allows horizontal sprite positioning optimized for a single row of sprites.
 =sprite-column(!col, !width = !sprite_image_default_width, !margin = !sprite_default_margin)
   +sprite-position(!col, 1, !width, 0px, !margin)
  
 // Allows vertical sprite positioning optimized for a single column of sprites.
 =sprite-row(!row, !height = !sprite_image_default_height, !margin = !sprite_default_margin)
   +sprite-position(1, !row, 0px, !height, !margin)
  
 // Allows vertical and horizontal sprite positioning from a grid of equal dimensioned sprites.
 =sprite-position(!col, !row = 1, !width = !sprite_image_default_width, !height = !sprite_image_default_height, !margin = !sprite_default_margin)
   !x = ((!col - 1) * -!width) - ((!col - 1) * !margin)
   !y = ((!row - 1) * -!height) - ((!row - 1) * !margin)
   :background-position= !x !y