External module in the NCBI Book DTD (and NCBI Collection DTD) that declares Parameter Entities of element class definitions to over-ride element classes in the base Suite
<!ENTITY % bookcustom-classes.ent PUBLIC "-//NLM//DTD NCBI Book DTD Over-ride Classes Module v2.3 20070202//EN" "bookcustom-classes.ent" >
bookcustom-modules.ent