additions  where_rules  BoundaryDim 
additions  where_rules  BoundaryType 
deletions  where_rules  WR41 
deletions  where_rules  WR42 
modifications  where_rules BoundaryType definition  Changed from sizeof(typeof(PolygonalBoundary)*['ifc4.ifcpolyline','ifc4.ifccompositecurve']) = 1 to sizeof(typeof(PolygonalBoundary)*['ifc4x1.ifcpolyline','ifc4x1.ifccompositecurve']) = 1 
modifications  where_rules BoundaryType definition  Changed from sizeof(typeof(PolygonalBoundary)*['ifc4x1.ifcpolyline','ifc4x1.ifccompositecurve']) = 1 to sizeof(typeof(PolygonalBoundary)*['ifc4x2.ifcpolyline','ifc4x2.ifccompositecurve']) = 1 
modifications  where_rules BoundaryType definition  Changed from sizeof(typeof(PolygonalBoundary)*['ifc4x2.ifcpolyline','ifc4x2.ifccompositecurve']) = 1 to sizeof(typeof(PolygonalBoundary)*['ifc4x3_rc3.ifcpolyline','ifc4x3_rc3.ifccompositecurve']) = 1 
The polygonal bounded half space is a special subtype of a half space solid, where the material of the half space used in Boolean expressions is bounded by a polygonal boundary. The base surface of the half space is positioned by its normal relative to the object coordinate system (as defined at the supertype IfcHalfSpaceSolid), and its polygonal (with or without arc segments) boundary is defined in the XY plane of the position coordinate system established by the Position attribute, the subtraction body is extruded perpendicular to the XY plane of the position coordinate system, that is, into the direction of the positive Z axis defined by the Position attribute.
The boundary is defined by a 2 dimensional polyline (or 2 dimensional composite curve, consisting of straight segments and circular arc segments) within the XY plane of the position coordinate system. The side of the surface which is in the half space is determined by the surface normal and the agreement flag. If the agreement flag is TRUE, then the subset is the one the normal points away from. If the agreement flag is FALSE, then the subset is the one the normal points into.
NOTE A polygonal bounded half space is not a subtype of IfcSolidModel, half space solids are only useful as operands in Boolean expressions.
Figure 1 illustrates a polygonal bounded half space.


Figure 1 — Polygonal half space geometry 
The polygonal bounded half space is used to limit the volume of the half space in Boolean difference expressions. Only the part that is defined by a theoretical intersection between the half space solid and an extruded area solid, defined by extruding the polygonal boundary, is used for Boolean expressions.
The PolygonalBoundary defines the 2D polyline which bounds the effectiveness of the half space in Boolean expressions. The BaseSurface is defined by a plane, and the normal of the plane together with the AgreementFlag defines the side of the material of the half space.
HISTORY New entity in IFC2x.
Informal Propositions:
#  Attribute  Type  Description 

IfcRepresentationItem  
LayerAssignment  SET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItems  Assignment of the representation item to a single or multiple layer(s). The LayerAssignments can override a LayerAssignments of the IfcRepresentation it is used within the list of Items. > IFC2x3 CHANGE The inverse attribute LayerAssignments has been added. > IFC4 CHANGE The inverse attribute LayerAssignment has been restricted to max 1. Upward compatibility for file based exchange is guaranteed.  
StyledByItem  SET [0:1] OF IfcStyledItem FOR Item  Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve. > IFC2x3 CHANGE The inverse attribute StyledByItem has been added.  
IfcGeometricRepresentationItem  
IfcHalfSpaceSolid  
1  BaseSurface  IfcSurface  Surface defining side of half space. 
2  AgreementFlag  IfcBoolean  The agreement flag is TRUE if the normal to the BaseSurface points away from the material of the IfcHalfSpaceSolid. Otherwise it is FALSE. 
Dim  INVALID  The space dimensionality of this class, it is always 3  
IfcPolygonalBoundedHalfSpace  
3  Position  IfcAxis2Placement3D  Definition of the position coordinate system for the bounding polyline ~~and the base surface~~. 
4  PolygonalBoundary  IfcBoundedCurve  Twodimensional ~~polyline~~ bounded curve, defined in the xy plane of the position coordinate system. > IFC2x3 CHANGE The attribute type has been changed from IfcPolyline to its supertype IfcBoundedCurve with upward compatibility for file based exchange. 
ENTITY IfcPolygonalBoundedHalfSpace SUBTYPE OF (IfcHalfSpaceSolid); Position : IfcAxis2Placement3D; PolygonalBoundary : IfcBoundedCurve; WHERE BoundaryDim : PolygonalBoundary.Dim = 2; BoundaryType : SIZEOF(TYPEOF(PolygonalBoundary) * [ 'IFC4X3_DEV_a1492713.IFCPOLYLINE', 'IFC4X3_DEV_a1492713.IFCCOMPOSITECURVE'] ) = 1; END_ENTITY;