updated documentation for new intersection iterator functionality

[[Imported from SVN: r4483]]

grid/common/intersectioniterator.hh

@@ -54,14 +54,13 @@ namespace Dune
      \image html  islocalref.png "IntersectionIterator in a locally refined mesh."
      \image latex islocalref.eps "IntersectionIterator in a locally refined mesh." width=\textwidth
 
-     Here the rule is the following: The IntersectionIterator deleivers the
-     intersection with an entity on the same level if possible or with an element
-     on a lower level which must be a leaf element in this case.
-
-     This means that if element c has an intersection with element a, a does
-     not necessarily have an intersection with element c. In the example above, a
-     would have an intersection with element b.
+     Here the rule is the following: The IntersectionIterator delivers all intersections
+     with elements on the same level and in addition intersections with all leaf elements
+     that are on a lower level.
 
+     According to this rule the intersection iterator started at a delivers an intersection
+     with b and c, the intersection itersection iterator started at c delivers intersections
+     with a and d and b has an intersection with a.
 
      <h2>Intersections, leaf grid and level grid</h2>
 
@@ -78,6 +77,13 @@ namespace Dune
      one can detect the position of an entity relative to the boundary. The
      following cases are possible.
 
+     <h2>Intersections and processor boundaries</h2>
+
+     At processor boundaries, i.e. when an element has an intersection with another element
+     in the sequential grid but this element is only stored in other processors the
+     intersection iterator stops but neither leafNeighbor(), levelNeighbor() nor boundary()
+     are true.
+
      <table>
      <tr>
      <td></td><td></td><td>neighbor()</td><td>boundary()</td><td>outside()</td>