/// <summary>
/// Add a volume (a region) defined by one or more shells `shellTags'. The
/// first surface loop defines the exterior boundary; additional surface loop
/// define holes. If `tag' is positive, set the tag explicitly; otherwise a
/// new tag is selected automatically. Return the tag of the volume.
/// </summary>
public static int AddVolume(int[] shellTags, int tag = -1)
{
var index = Gmsh_Warp.GmshModelGeoAddVolume(shellTags, shellTags.LongLength, tag, ref Gmsh._staticreff);
Gmsh.CheckException(MethodBase.GetCurrentMethod().MethodHandle);
return(index);
}