Contains the stylesheet state for a single scene. This includes both the Stylesheets defined on the Scene itself as well as a map of stylesheets for "style"s defined on the Node itself. These containers are kept in the containerMap, key'd by the Scene to which they belong.

One of the key responsibilities of the StylesheetContainer is to create and maintain an admittedly elaborate series of caches so as to minimize the amount of time it takes to match a Node to its eventual StyleHelper, and to reuse the StyleHelper as much as possible.

Initially, the cache is empty. It is recreated whenever the userStylesheets on the container change, or whenever the userAgentStylesheet changes. The cache is built up as nodes are looked for, and thus there is some overhead associated with the first lookup but which is then not repeated for subsequent lookups.

The cache system used is a two level cache. The first level cache simply maps the classname/id/styleclass combination of the request node to a 2nd level cache. If the node has "styles" specified then we still use this 2nd level cache, but must combine its selectors with the selectors specified in "styles" and perform more work to cascade properly.

The 2nd level cache contains a data structure called the Cache. The Cache contains an ordered sequence of Rules, a Long, and a Map. The ordered sequence of selectors are the selectors that *may* match a node with the given classname, id, and style class. For example, selectors which may apply are any selector where the simple selector of the selector contains a reference to the id, style class, or classname of the Node, or a compound selector whose "descendant" part is a simple selector which contains a reference to the id, style class, or classname of the Node.

During lookup, we will iterate over all the potential selectors and discover if they apply to this particular node. If so, then we toggle a bit position in the Long corresponding to the position of the selector that matched. This long then becomes our key into the final map.

Once we have established our key, we will visit the map and look for an existing StyleHelper. If we find a StyleHelper, then we will return it. If not, then we will take the Rules that matched and construct a new StyleHelper from their various parts.

This system, while elaborate, also provides for numerous fast paths and sharing of data structures which should dramatically reduce the memory and runtime performance overhead associated with CSS by reducing the matching overhead and caching as much as possible. We make no attempt to use weak references here, so if memory issues result one work around would be to toggle the root user agent stylesheet or stylesheets on the scene to cause the cache to be flushed.