public interface SCSpriteConfig extends SCImgURL
skinning overview  documentation.  The Smart GWT
 framework supports the SCSpriteConfig format for sprited images.
 spriteConfigs have the following
 format:
 "sprite:<image
 URL>;offset:<Left>,<Top>;size:<Width>,<Height>;cssClass:<className>"
 
This format allows developers to specify the image source and the native size and offset of the sprite within the image.
 The media to load will be retrieved from the specified image URL. Standard  SCImgURL directory prefixes such as "[SKIN]" can be included in this URL.
 An explicit URL
 is not required - developers may instead specify a css class which can include an explicit background-image
 attribute. 
 The offset: property specifies the left and top coordinate to apply to the  composite image
 element such that the desired sprite is visible. The size:  property indicates the size of the sprite in
 pixels.
 For example, a sprite configuration of  "sprite:composite.png;offset:0,-20;size:20,20;"
 would load the image file "composite.png", and display a 20 pixel square from it. The origin of the larger image would
 be offset vertically by -20px, so the sprite actually visible to the user would have its y-origin at 20px within the
 larger image.
 As with the image URL, explicit size and offset are not required - a developer may use css properties
 (width, height and background-offset) from the specified class to specify the
 specific sprite to display. 
 The cssClass: denotes the css class to apply to the rendered element
 displaying the sprite. This is optional - a sprite can be specified with an image URL and explicit sizing and offset
 coordinates, in which case no css class is actually required.
 (Of course for a valid sprite, it is expected that the
 image URL and size are specified either explicitly in the string, or within the css class definition. If the offset is
 omitted, it will be assumed to be zero on both axes). 
 Sprites will scale automatically. If a spriteConfig is used to
 provide an image for an icon and some other property is used to configure the drawn size of the icon in question (Button.iconSize,for example), the sprite image will be scaled to render
 at the appropriate size. 
 Sprited image configuration and "stateful" images
 Many image URLs in Smart GWT
 are "stateful", meaning that variants of the image should be  displayed to the user depending on the current state of
 the widget.  (For example a custom button icon may be displayed on roll over, or a selection checkbox icon in a treeGrid  may appear disabled for unselectable nodes).
 
There are a couple of approaches to display stateful versions of sprited images.
 Wherever SCStatefulImgConfig objects are supported, a developer may include  spriteConfig strings as
 entries for specific states.
 For example, the following SCStatefulImgConfig definition would display different
 sprites from "compositeImg.png" for base and "Over" states:
   {
 _base:"sprite:compositeImg.png;offset:-100,-100;size:20,20", 
          
     Over:"sprite:compositeImg.png;offset:-100,-120;size:20,20" }
 Alternatively, if a
 property that behaves as the base URL for a stateful image  (such as Button.icon) is set to a sprite configuration string,  the framework will use the state name as a suffix to apply to
 the source URL or the css class specified in the sprite.
 As with standard stateful images, if a URL was specified for the sprite, the stateful suffix
 will be applied with a preceding "_" character.
 So if the state "Over" was applied to a sprite configuration of 
 "sprite:compositeImg.png;offset:100,100;size:20,20", the generated HTML would attempt to load an image from
 the URL "compositeImg_Over.png" (and display a sprite from that image with the specified size/offset).
 If a class name was specified in the sprite, the stateful suffix would be appended with no leading underscore, similar
 to how state suffixes are applied to the 
 baseStyle of a StatefulCanvas.
 For example a sprite config of "sprite:cssClass:buttonIcon"
 would display  styling from "buttonIconOver" when the "Over" state was applied.