This .NET class wraps the AcBrElement2d ObjectARX class. 

The Element2d class is the interface class for linear, first-order two-dimensional elements in a mesh. This class defines the functions that are pertinent to the 2D element level of a mesh, and cannot be directly set by the user as the initialization requirements are only available internally at the time of a call to Mesh2d.Generate(). 

A 2D element is a planar approximation of a subset of a bounded surface and thus has no directly associated geometry. It represents a polygonal (that is, closed) set of at least three coplanar nodes in a mesh (note that the associated node coordinates can be used to instantiate a Plane). A mapping back to the original brep topology is provided in the form of a backpointer to the face which generated this element (compare MeshEntity.EntityAssociated). 

This class generally is accessed by the user via a mesh element traverser. The only way to delete the element referenced by this class from the mesh data cache is to delete the mesh object that owns it, or to regenerate the mesh.

Autodesk.AutoCAD.BoundaryRepresentation.MeshEntity
    Autodesk.AutoCAD.BoundaryRepresentation.Element
        Autodesk.AutoCAD.BoundaryRepresentation.Element2d

Public sealed Class Element2d
Inherits Element

public sealed class Element2d : Element;

Element, Mesh2dElement2dCollection