SP supports the Extended Naming Rules as specified in Annex J of ISO 8879:1986 (added by the 1996 technical corrigendum).
If the SGML declaration is omitted and there is no applicable SGMLDECL entry in a catalog, the following declaration will be implied:
<!SGML "ISO 8879:1986" CHARSET BASESET "ISO 646-1983//CHARSET International Reference Version (IRV)//ESC 2/5 4/0" DESCSET 0 9 UNUSED 9 2 9 11 2 UNUSED 13 1 13 14 18 UNUSED 32 95 32 127 1 UNUSED CAPACITY PUBLIC "ISO 8879:1986//CAPACITY Reference//EN" SCOPE DOCUMENT SYNTAX SHUNCHAR CONTROLS 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 127 255 BASESET "ISO 646-1983//CHARSET International Reference Version (IRV)//ESC 2/5 4/0" DESCSET 0 128 0 FUNCTION RE 13 RS 10 SPACE 32 TAB SEPCHAR 9 NAMING LCNMSTRT "" UCNMSTRT "" LCNMCHAR "-." UCNMCHAR "-." NAMECASE GENERAL YES ENTITY NO DELIM GENERAL SGMLREF SHORTREF SGMLREF NAMES SGMLREF QUANTITY SGMLREF ATTCNT 99999999 ATTSPLEN 99999999 DTEMPLEN 24000 ENTLVL 99999999 GRPCNT 99999999 GRPGTCNT 99999999 GRPLVL 99999999 LITLEN 24000 NAMELEN 99999999 PILEN 24000 TAGLEN 99999999 TAGLVL 99999999 FEATURES MINIMIZE DATATAG NO OMITTAG YES RANK YES SHORTTAG YES LINK SIMPLE YES 1000 IMPLICIT YES EXPLICIT YES 1 OTHER CONCUR NO SUBDOC YES 99999999 FORMAL YES APPINFO NONE>
with the exception that all characters that are neither significant nor shunned will be assigned to DATACHAR.
A character in a base character set is described either by giving its number in a universal character set, or by specifying a minimum literal. The first 65536 character numbers in the universal character set are assumed to be the same as in Unicode 2.0 (ISO/IEC 10646). The remaining character numbers can be assigned in any way convenient.
The public identifier of a base character set can be associated with an entity that describes it by using a PUBLIC entry in the catalog entry file. The entity must be a fragment of an SGML declaration consisting of the portion of a character set description, following the DESCSET keyword, that is, it must be a sequence of character descriptions, where each character description specifies a described character number, the number of characters and either a character number in the universal character set, a minimum literal or the keyword UNUSED. Character numbers in the universal character set can be as big as 99999999.
In addition SP has built in knowledge of many character sets. These are identified using the designating sequence in the public identifier. The following designating sequences are recognized:
The public identifier for a public concrete syntax can be associated with an entity that describes using a PUBLIC entry in the catalog entry file. The entity must be a fragment of an SGML declaration consisting of a concrete syntax description starting with the SHUNCHAR keyword as in an SGML declaration. The entity can also make use of the following extensions:
The public identifier for a public capacity set can be associated with an entity that describes using a PUBLIC entry in the catalog entry file. The entity must be a fragment of an SGML declaration consisting of a sequence of capacity names and numbers.