Traversers are used to walk through the topological structure of the solid. They are either global or hierarchical.
Global traversers (such as AcBrBrepFaceTraverser and AcBrBrepEdgeTraverser) provide the ability to traverse all of the topological objects in the solid (complexes, shells, faces, edges, vertices).
Hierarchical traversers provide the ability to walk through local areas of the solid, either top-down or bottom-up. Several of these traversers, such as AcBrLoopEdgeTraverser and AcBrLoopVertexTraverser, also provide queries to distinguish between multiple uses of the same edge or vertex.
For example, an edge has no inherent knowledge of which face it is being referenced from. So, the parameter curve data, which depends on the underlying surface on which the edge is defined, is queried from AcBrLoopEdgeTraverser.
Downward hierarchical traversers give access to the topologically adjacent subentities that make up the boundary of a given topological object (that is, the traverser list owner).