anchor.diff:  which defines mostly common services that are used by client side,
   but implemented in the server side.
   
  -* Runtime Plugins
   * VFS (Virtual File System)
  -
  -TODO
  ++
  +The Virtual File System API provides a set of IO related features for client-side components.
   
   UberFire Client API Concepts
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  
positive.code: ** Panel definitions
  ** Part definitions
  
  TODO
  
  UberFire Metadata Concepts
  ~~~~~~~~~~~~~~~~~~~~~~~~~~
  
  
negative.code: These concepts are expressed in the `uberfire-commons` package,
  which contains a mix of server-only definitions shared client/server definitions.
  
  * Data
   ** Pair, a generic 2-tuple (client + server)
   ** Triple, a generic 3-tuple (client + server)
   ** Cacheable, interface that provides explicit visibility of cached data.
  * Lock Service (server-only)
  +
  Common service interface to implement locks. Provides a `Thead` default implementation.
  * Clustering (server-only, see also UberFire I/O)
  +
  A general clustering abstraction that provides a combination of `Lock` and `Message` services in a clustered environment (multiple computers).
  * Messaging
  +
  General purpose messaging abstraction (server-only, distinct from Errai Bus messages). Currently implemented by IO clustered setup.
  
  ** Message
  +
  Message is basically a composition of a `MessageType` and a `Map` of arbitrary values.
  ** AsyncCallback
  +
  Async callback mechanism used to by call and wait messaging broadcast. Currently used to sync file systems in the cluster during startup.
  ** MessageHandler
  +
  Interface that process messages, messages are routed to MessageHandler by `MessageHandlerResolver`.
  ** MessageHandlerResolver
  +
  Simple routing mechanism to `MessageHandler` 's.
  ** MessageService
  +
  Common service interface to implement broadcast (sync/async) and participant specific messaging exchange.
  ** MessageType
  +
  Simple message classification. Usually used by `MessageHandlerResolver` in order to route a message to a proper `MessageHandler`.
  
  * CDI Startup Beans (the @Startup annotation) (server-only)
  * PortablePreconditions (client + server), a collection of static methods for checking common preconditions (reference not null, list not empty, etc.)
  