Located at the very top of the document, just after VERSION.
This doesn't change much between documents, so I tend to use the same block in all of mine. Some of the symbols listed, such as CAT_ are now deprecated and will not be included or examined in this specification.
NS_ : NS_DESC_ BO_TX_BU_ BA_DEF_DEF_ BA_DEF_ BA_ CM_ VAL_ VAL_TABLE_ SGTYPE_ SGTYPE_VAL_ SG_MUL_VAL_ SIG_VALTYPE_ SIGTYPE_VALTYPE_ SIG_GROUP_ CAT_DEF_ CAT_ FILTER EV_DATA_ ENVVAR_DATA_ SIG_TYPE_REF_ BA_REL_ BA_SGTYPE_ BA_DEF_REL_ BA_DEF_SGTYPE_ BA_DEF_DEF_REL_ BU_SG_REL_ BU_EV_REL_ BU_BO_REL_