This implementation follows the description of Doubly-Connected Edge Lists in the book "Computational Geometry", de Berg et al.

This class exposes one vertex of the mesh. Other mesh components can be found by navigating the DCEL data structures beginning at Vertex.

For convenience, component lists (Vertices, Edges and Faces) are automatically generated when required. Whenever the mesh is modified (components are added or removed), the flag Dirty must be set. Then the component list are automatically recreated the next time they are accessed.

Handling Tags: The DCEL data structures (DcelVertex, DcelEdge and DcelFace) have "tags" (integer properties) which can be used to mark components when navigating or modifying the mesh. This tags can be used by different operations that act on the mesh.