Those elements that may mix with data characters inside a chemical structure (<chem-struct>)
<!ENTITY % chem-struct-elements "| %access.class; | %address-link.class; | %break.class; | %emphasis.class; | %label.class; | %list.class; | %math.class; | %simple-display.class; | %simple-link.class; | %subsup.class; " >
display.ent