anchor.diff:  restriction is, to make the user aware of the consequences that removing a frame
   might have for the graph structure as a whole.
   
  -
  -#### Loading Envire Plugins
  -Envire Plugins provide ...
  -TODO
  -TODO
  -TODO
  -TODO
  -#### Creating Items
  +=== Plugins
  + TODO
  +
  +=== Items
  +
  +==== Creating Items
   Before an item can be added to a frame, it has to be loaded using the ``ClassLoader``.
  -```
  +[source,c++]
  +----
   #include <envire_core/plugin/ClassLoader.hpp>
   #include <envire_core/items/Item.hpp>
   #include <octomap/AbstractOcTree.h>
  -```
  -```
  +----
  +
  +[source,c++]
  +----
   envire::core::Item<boost::shared_ptr<octomap::AbstractOcTree>>::Ptr octree;
   ClassLoader* loader = ClassLoader::getInstance();
   if(!loader->createEnvireItem("envire::core::Item<boost::shared_ptr<octomap::AbstractOcTree>>", octree))
  
positive.code: = EnviRe Core Documentation
  
  :toc:
  
  == Build and Test Status
  
  
negative.code: TreeViews use vertex_descriptors instead of FrameIds to reference frames because
  vertex_descriptors can be hashed in constant time (they are just pointers).
  
  ==== Creating Tree Views
  TreeViews can be created by calling ``getTree()`` and providing a root node.
  [source,c++]
  ----
  EnvireGraph g;
  const FrameId root("root");
  TreeView view = g.getTree(root);
  ----
  
  Note that the view will most likely be copied on return. If the tree is large
  you might want to avoid that copy and pass an empty view as out-parameter instead:
  [source,c++]
  ----
  TreeView view2;
  g.getTree(root, &view2);
  ----
  
  ==== Updating Tree Views
  
  By default, a tree view shows a snapshot of the graph. I.e. if the graph changes,
  the changes will not be visible in the view. The view or parts of it might
  become invalid when vertices or edges are removed from the graph.
  To avoid this, you can request a self-updating tree view:
  [source,c++]
  ----
  g.getTree(root, true, &view);
  ----
  
  The view has three signals ``crossEdgeAdded``, ``edgeAdded`` and ``edgeRemoved``
  that will be emitted whenever the tree view changes.
  
  
  == Maintenance and development
  DFKI GmbH - Robotics Innovation Center
  [link=https://robotik.dfki-bremen.de/en/startpage.html]
  image::https://github.com/envire/envire.github.io/raw/master/images/dfki_logo.jpg[DFKI Logo]
  