A predefined item is a qualified name given to a style or font which is determined within the data exchange specification by convention on using the Name attribute value (in contrary to externally defined items, which are agreed by an external source). 

The next instance diagram explains the use of IfcStyledItem and IfcPresentationLayerWithStyle to apply presentation styles.

• EXAMPLE: The assignment of style information by a styled item and a presentation layer with style.

Since the presentation styles are different, IfcCurveStyle and IfcSurfaceStyle, both are applied to the geometric representation item. 

The next instance diagram explains the override of IfcPresentationLayerWithStyle by IfcStyledItem to apply presentation styles.

• EXAMPLE: The assignment of style information by a styled item and a presentation layer with style.

Since the presentation styles for curve style are provided by both, the IfcCurveStyle provided by the IfcStyledItem overrides the IfcCurveStyle provided by the IfcPresentationLayerWithStyle. 

The convention on using the Name value is defined at the subtypes of IfcPreDefinedItem and is part of the specification.