This grammar is intended to help make SGML more comprehensible for formal manipulation. For this reason, a number of simplifications have been undertaken, which are described below in section . These simplifications may cause this grammar to accept some documents not accepted by the official grammar. As far as is known, however, the grammar provided here will recognize any valid SGML document in the TEI Interchange Format.

For ease in relating this grammar to the formal grammar defined in ISO 8879, comments for each group here give the numbers of the related productions in that grammar. Where the changes to SGML syntax suggested by the SGML working group in its document ISO/IEC JTC1 / SC18 / WG8 / N1035 would affect the productions here, that fact is noted after the affected production.

Each sub-grammar given here has been checked for ambiguity with bison, a public-domain workalike for yacc, and flex, a public-domain workalike for lex. The bison and flex source files, including the simple modifications needed to implement the recognition-mode stack, are available from the TEI.

The SGML declaration grammar and the DTD grammar have no ambiguities. The document grammar has several ambiguities, which are discussed in section . Notation

The notation used here is based on notations commonly used in writing context-free grammars. All non-terminals are written as single tokens. ::= is defined as a b instance of a followed by instance of b, possibly separated by white space; white space may be required if a and b cannot otherwise be delimited a | b instance of a or instance of b a || binstance of a followed immediately by an instance of b, without any intervening white space /* */comment; right-hand sides comprising only a comment are used to call attention to productions in which the left-hand sides can reduce to the empty string //comment; runs to end of line All non-quoted strings are non-terminals. All terminals are quoted. Grammar for SGML Document (Overview)

An SGML document is preceded by an SGML declaration and a prolog comprising one or more document-type declarations. It may be accompanied by one or more subdocument entities, text entities, non-SGML entities, etc., but for simplicity these last are not discussed here. SGMLdoc ::= SGMLdeclaration prolog docinstance // cf. 1, 2

The grammars for the SGML declaration, the prolog, and the document instance are provided in the following three sections. Grammar for SGML Declaration

This grammar is substantively the same as that in ISO 8879; it does not reflect the restrictions placed on SGML declarations for TEI-conformant documents. ' /* ** Strictly speaking, the blank in 'ISO 8879:1986' may be ** replaced by any amount or type of white space. */ charset ::= baseset descset // cf. 173 | charset baseset descset baseset ::= 'BASESET' pubid // cf. 174 /* For pubid, see Common Constructs below */ descset ::= 'DESCSET' chardesc // cf. 175 | descset chardesc chardesc ::= NUMBER NUMBER NUMBER // cf. 176-179 | NUMBER NUMBER LITERAL | NUMBER NUMBER 'UNUSED' /* ** The first two numbers in chardesc identify starting point ** and a number of characters in the described character set; ** the third number gives the starting position for that run ** in the base set; a literal provides a description of the ** character(s); 'UNUSED' marks the run as unused. */ capacity ::= 'PUBLIC' pubid // cf. 180 | 'SGMLREF' caplist caplist ::= capname NUMBER | caplist capname NUMBER capname ::= 'TOTALCAP' | 'ENTCAP' | 'ENTCHCAP' | 'ELEMCAP' | 'GRPCAP' | 'EXGRPCAP' | 'EXNMCAP' | 'ATTCAP' | 'ATTCHCAP' | 'AVGRPCAP' | 'NOTCAP' | 'NOTCHCAP' | 'IDCAP' | 'IDREFCAP' | 'MAPCAP' | 'LKSETCAP' | 'LKNMCAP' // cf. Fig. 5 scope ::= 'DOCUMENT' | 'INSTANCE' // cf. 181 syntax ::= 'PUBLIC' pubid // cf. 182-183 | 'PUBLIC' pubid switchlist | 'SHUNCHAR' shunchars // cf. 184 charset // cf. 185 'FUNCTION' // cf. 186 'RE' NUMBER 'RS' NUMBER 'SPACE' NUMBER funlist 'NAMING' // cf. 189 'LCNMSTRT' LITERAL 'UCNMSTRT' LITERAL 'LCNMCHAR' LITERAL 'UCNMCHAR' LITERAL 'NAMECASE' 'GENERAL' yesno 'ENTITY' yesno 'DELIM' // cf. 190-92 'GENERAL' 'SGMLREF' gendelim 'SHORTREF' srdelim 'NAMES' 'SGMLREF' nameset // cf. 193 'QUANTITY' 'SGMLREF' quantityset // cf. 194 /* ** Document WG8 / N1035 suggests allowing multiple literals ** after each keyword in the NAMING section; this may be ** effected by adding the non-terminal literalset after each ** LITERAL. */ switchlist ::= 'SWITCHES' NUMBER NUMBER // cf. 183 | switchlist NUMBER NUMBER shunchars ::= 'NONE' // cf. 184 | shunlist shunlist ::= 'CONTROLS' | NUMBER | shunlist NUMBER funlist ::= NAME funclass NUMBER // cf. 186-187 | funlist NAME funclass NUMBER funclass ::= 'FUNCHAR' | 'MSICHAR' | 'MSOCHAR' // cf. 188 | 'MSSCHAR' | 'SEPCHAR' gendelim ::= /* nil */ // cf. 191 | gendelim delimname LITERAL delimname ::= 'AND' | 'COM' | 'CRO' // cf. Fig. 3 | 'DSC' | 'DSO' | 'DTGC' // clause 9.6 | 'DTGO' | 'ERO' | 'ETAGO' | 'GRPC' | 'GRPO' | 'LIT' | 'LITA' | 'MDC' | 'MDO' | 'MINUS' | 'MSC' | 'NET' | 'OPT' | 'OR' | 'PERO' | 'PIC' | 'PIO' | 'PLUS' | 'REFC' | 'REP' | 'RNI' | 'SEQ' | 'SHORTREF' | 'STAGO' | 'TAGC' | 'VI' srdelim ::= 'SGMLREF' literalset // cf. 192 | 'NONE' literalset literalset ::= /* nil */ | literalset LITERAL nameset ::= /* nil */ | nameset sgmlname NAME /* ** WG8 / N1035 substitutes a LITERAL for the NAME of the ** preceding rule; the value must be a NAME in the declared ** concrete syntax, but it need not be a legal name in the ** reference concrete syntax. */ sgmlname ::= 'ANY' | 'ATTLIST' | 'CDATA' | 'CONREF' | 'CURRENT' | 'DEFAULT' | 'DOCTYPE' | 'ELEMENT' | 'EMPTY' | 'ENDTAG' | 'ENTITIES' | 'ENTITY' | 'FIXED' | 'ID' | 'IDLINK' | 'IDREF' | 'IDREFS' | 'IGNORE' | 'IMPLIED' | 'INCLUDE' | 'INITIAL' | 'LINK' | 'LINKTYPE' | 'MD' | 'MS' | 'NAME' | 'NAMES' | 'NDATA' | 'NMTOKEN' | 'NMTOKENS' | 'NOTATION' | 'NUMBER' | 'NUMBERS' | 'NUTOKEN' | 'NUTOKENS' | 'O' | 'PCDATA' | 'PI' | 'POSTLINK' | 'PUBLIC' | 'RCDATA' | 'RE' | 'REQUIRED' | 'RESTORE' | 'RS' | 'SDATA' | 'SHORTREF' | 'SIMPLE' | 'SPACE' | 'STARTTAG' | 'SUBDOC' | 'SYSTEM' | 'TEMP' | 'USELINK' | 'USEMAP' quantityset ::= /* nil */ | quantityset quantity NUMBER quantity ::= 'ATTCNT' | 'ATTSPLEN' | 'BSEQLEN' // Cf. | 'DTAGLEN' | 'DTEMPLEN' | 'ENTLVL' // Fig. 6 | 'GRPCNT' | 'GRPGTCNT' | 'GRPLVL' | 'LITLEN' | 'NAMELEN' | 'NORMSEP' | 'PILEN' | 'TAGLEN' | 'TAGLVL' yesno ::= 'NO' | 'YES' count ::= 'NO' | 'YES' NUMBER appinfo ::= 'NONE' | LITERAL // cf. 199 /* ** The literal string is restricted to letters, digits, ** whitespace, and 'specials': viz. any of ** ' ( ) + , - . / : = ? */ ]]> Grammar for DTD

An SGML prolog is composed of one or more document type declarations; if multiple DTDs are present, the SGML declaration must include CONCUR YES in the FEATURES section. A document type declaration names the root element of the document and declares (in an external file, in a DTD subset, or both) elements, attributes, notations, and entities used in the document instance. Interspersed with these declarations may be comments and processing instructions. ' | '' | '' | '' dtdsubset ::= /* */ // cf. 112, 113, 114 | dtdsubset elementdecl | dtdsubset attlistdecl | dtdsubset notationdecl | dtdsubset entitydecl | dtdsubset commdecl | dtdsubset procinst /* Element Declarations */ // cf. 116 elementdecl ::= '' elemtype ::= NAME // cf. 117, 30, 72 | '(' namegrp ')' namegrp ::= andnames // cf. 69, 131 | ornames | seqnames seqnames ::= NAME | seqnames ',' NAME ornames ::= NAME '|' NAME | ornames '|' NAME andnames ::= NAME '&' NAME | andnames '&' NAME minimiz ::= min min // cf. 122-124 min ::= 'O' | '-' contentdecl ::= 'CDATA' // cf. 125, 126 | 'RCDATA' | 'EMPTY' | 'ANY' exceptions | model exceptions model ::= '(' tokengrp ')' // cf. 127 | '(' tokengrp ')?' | '(' tokengrp ')*' | '(' tokengrp ')+' tokengrp ::= seqtokens // cf. 127 | ortokens | andtokens seqtokens ::= token | seqtokens ',' token ortokens ::= token '|' token | ortokens '|' token andtokens ::= token '&' token | andtokens '&' token token ::= '#PCDATA' // cf. 128-130 | NAME || occurrence | model occurrence ::= /* nil */ // cf. 132 | '?' | '*' | '+' exceptions ::= exclusions inclusions // cf. 138-140 exclusions ::= /* nil */ | '-(' namegrp ') inclusions ::= /* nil */ | '+(' namegrp ')' /* Attribute List Declarations */ attlistdecl ::= '' // Cf. 141 associated ::= elemtype | assocnotatn assocnotatn ::= '#NOTATION' NAME // Cf. 149.1 | '#NOTATION' '(' namegrp ')' attdeflist ::= attdef // Cf. 142 | attdeflist attdef attdef ::= NAME valtype default // Cf. 143-44 valtype ::= 'CDATA' | // Cf. 145 | 'ENTITY' | 'ENTITIES' | 'ID' | | 'IDREF' | 'IDREFS' | 'NAME' | 'NAMES' | 'NMTOKEN' | 'NMTOKENS' | 'NUMBER' | 'NUMBERS' | 'NUTOKEN' | 'NUTOKENS' | 'NOTATION' '(' namegrp ')' | '(' nmtokgrp ')' nmtokgrp ::= nmtokcom | nmtokbar | nmtokamp // Cf. 68, 131 nmtokcom ::= nametoken | nmtokcom ',' nametoken nmtokbar ::= nametoken '|' nametoken | nmtokbar '|' nametoken nmtokamp ::= nametoken '&' nametoken | nmtokamp '&' nametoken nametoken ::= NAME | NUMBER | NUMTOKEN default ::= value // Cf. 147 | '#FIXED' value | '#REQUIRED' | '#CURRENT' | '#CONREF' | '#IMPLIED' /* For value, see Common Constructs below */ /* Notation Declarations */ // cf. 148-49, 41 notationdecl ::= '' /* Entity Declarations */ // cf. 101-04 entitydecl ::= '' | '' | '' /* ** Strictly, any white space is acceptable after the % ** in a parameter entity declaration, not just a single ** space. */ enttext ::= LITERAL // cf. 105-08 | 'CDATA' LITERAL | 'SDATA' LITERAL | 'PI' LITERAL | 'STARTTAG' LITERAL | 'ENDTAG' LITERAL | 'MS' LITERAL | 'MD' LITERAL | extid enttype enttype ::= /* */ // cf. 108-109, 149.2 | 'SUBDOC' | 'CDATA' NAME | 'CDATA' NAME '[' attspecset ']' | 'NDATA' NAME | 'NDATA' NAME '[' attspecset ']' | 'SDATA' NAME | 'SDATA' NAME '[' attspecset ']' /* For attspecset, see Common Constructs below. */ extid ::= 'SYSTEM' // cf. 73 | 'SYSTEM' sysid | 'PUBLIC' pubid | 'PUBLIC' pubid sysid /* For pubid, see Common Constructs below */ sysid ::= LITERAL // cf. 75 ]]> Grammar for Document Instance

The SGML document instance is composed of one element (the root element), followed optionally by white space, comments, and processing instructions. The root element, like any other, has a start-tag, content, and an end-tag, or only a start-tag (if it is empty). The specific sort of content recognized within an element depends upon its element declaration. ' // cf. 14, 28-30 | '<(' namegrp ')' || NAME attspecset '>' /* ** The name group is used only if the SGML declaration ** specifies CONCUR YES. ** For attspecset, see Common Constructs below. */ content ::= mixedcontent // cf. 24 | elemcontent | rcdata | cdata mixedcontent ::= /* nil */ // cf. 25 | mixedcontent STRING | mixedcontent element | mixedcontent misccontent elemcontent ::= /* nil */ // cf. 26 | elemcontent element | elemcontent misccontent cdata ::= STRING // cf. 47 | cdata STRING rcdata ::= STRING // cf. 46 | rcdata STRING /* ** White space is ignored between elements in element content, ** but not in mixed content. In CDATA and RCDATA, start-tag ** delimiters are not recognized. In CDATA, entity reference ** delimiters are not recognized. An element's content model ** determines whether it is scanned for mixed content, element ** content, CDATA content, or RCDATA content. */ misccontent ::= commdecl // cf. 27 | procinst /* ** For commdecl and procinst, see Common Constructs below. ** Omitted here for simplicity are short-reference and ** link-set use declarations and short references (which are ** not allowed in TEI interchange format), entity references ** (which are assumed to be handled by the lexical scanner), ** and marked-section declarations (also in lexical ** scanner). */ end-tag ::= '' // cf. 19, 21 | '' | '' /* ** The name group is used only if the SGML declaration ** specifies CONCUR YES. ** N.B. The last form (short end-tag) is not allowed in the ** TEI Interchange Format. */ ]]>

The document-instance grammar just given contains two sets of formal ambiguities. One set concerns the distinction among mixed content, element content, RCDATA, and CDATA, which depends not on the document content but on the definition of the element within which they appear. These conflicts can be eliminated by eliminating the distinction and assigning the task of distinguishing content type (and alerting the lexical analyzer to modify its behavior) to the semantic rules of the parser, rather than to the syntax.

The second set of ambiguities arises in connection with start-tags: after a start-tag, empty elements are complete, others not, and the ambiguity can be resolved only by consulting the DTD, not by lookahead. Such conflicts can be avoided by defining document content as an unstructured sequence of start-tags, end-tags, and data content; the parser's semantic actions must enforce the pairing and nesting of start- and end-tags and the distinction between empty and non-empty elements. Despite the ambiguities, the grammar given here seems to express the nature of SGML documents more clearly than the unambiguous alternative and so has not been changed; the changes needed to eliminate the parsing conflicts are these: delete element, mixedcontent, elemcontent, cdata, and rcdata. redefine docinstance and content as follows: Applications using this simplification must distinguish mixed content, element content, RCDATA, and CDATA using other methods than document syntax. They can check the appropriate matching of start- and end-tags using a simple element stack with provision for empty elements. Some SGML normalizers provide explicit end-tags for empty elements to simplify this task. Common Syntactic Constructs

This section defines syntactic constructions used in more than one of the three preceding grammar fragments. ' // cf. 91, 92 | '' commseq ::= /* nil */ | commseq '--' STRING '--' procinst ::= '' // cf. 44 attspecset ::= /* nil */ // cf. 31 | attspecset attspec attspec ::= NAME '=' value // cf. 32 | value /* ** NAME may be omitted only if the attribute has an ** enumerated range of values and the value is an unquoted ** name token. */ value ::= LITERAL // Cf. 33 | NAME | NUMBER | NUMTOKEN pubid ::= LITERAL // cf. 74, 76 /* ** The literal string is restricted to letters, digits, ** whitespace, and 'specials': viz. any of ** ' ( ) + , - . / : = ? */ ]]> Lexical Scanner

The grammar given above assumes a lexical scanner which scans for the terminal strings represented here in quotes scans for certain other token types (listed below) handles white space and some comments without returning them recognizes and expands entity references appropriately without notifying the parser

N.B. the literals given here for delimiters, keywords, and in the definitions of character classes and character types, are those used in the reference concrete syntax of SGML; a full SGML parser must be able to use other concrete syntaxes.

The token types to be returned by the lexical scanner include (in addition to the literals used in the grammars above): name number numtoken literal string These are printed in all caps in the grammar and are defined thus: NAME ::= letter // Cf. 55 | NAME || letter | NAME || digit | NAME || othernamech NUMBER ::= digit // cf. 56 | NUMBER || digit NUMTOKEN ::= digit || letter // cf. 58 | digit || othernamech | NUMTOKEN || letter | NUMTOKEN || digit | NUMTOKEN || othernamech LITERAL ::= "'" || STRING || "'" // Cf. 66, 76, 34 | '"' || STRING || '"' STRING ::= /* */ | STRING || character character ::= letter | digit | othercharacter letter ::= 'a' | 'b' | 'c' | 'd' ... | 'z' | 'A' | 'B' | 'C' | 'D' ... | 'Z' digit ::= '0' | '1' | '2' | '3' ... | '9' othernamech ::= '-' | '.' whitespace ::= space | tab | record-end | record-start space ::= /* as defined in SGML declaration */ tab ::= /* as defined in SGML declaration */ record-end ::= /* as defined in SGML declaration */ record-start ::= /* as defined in SGML declaration */ othercharacter ::= /* as defined in SGML declaration */

This list of primitive token types differs slightly from that of ISO 8879, which defines names, numbers, name tokens, and number tokens as overlapping sets of tokens distinguished by context. The redefinition provided here assigns each string to a single class and thus allows a simpler lexical analyzer. The terms in ISO 8879 correspond to those here in the following way: ISO 8879 name = NAME ISO 8879 number = NUMBER ISO 8879 name token = NAME | NUMBER | NUMTOKEN ISO 8879 number token = NUMBER | NUMTOKEN

The grammar given above assumes that the lexical scanner will recognize and handle entity references and marked sections. Entity references take one of the following forms (parameter entities within the DTD and within marked section declarations, general entities within document content and attribute values):

The processing of an entity reference may involve scanning its replacement text for delimiters, passing its content to the parser without scanning for delimiters, opening a new file if the entity is external to the SGML document, and other special processing not described here.

Marked sections take the following forms (n.b. the marked section keywords may be replaced by parameter entity references). ' mscdata ::= '' msrcdata ::= '' msinclude ::= '' /* Marked Section keywords */ ignore ::= kwcdata 'IGNORE' kwcdata | ignore 'IGNORE' kwcdata kwcdata ::= kwrcdata 'CDATA' kwrcdata | kwcdata 'CDATA' kwrcdata kwrcdata ::= include 'CDATA' include | kwrcdata 'CDATA' include include ::= /* nothing */ | include 'INCLUDE' | include 'TEMP' /* ** Multiple keywords may appear; rank order is IGNORE, ** CDATA, RCDATA, INCLUDE. TEMP is also legal but has ** no effect. */ chardata ::= /* characters returned to parser as character data, regardless of what delimiters are present */ rchardata ::= /* characters scanned for entity references, and then returned to parser as character data, regardless of what other delimiters are present */ scandata ::= /* characters scanned and returned to parser as normal */ anything ::= /* characters scanned only for ']]' || '>' and not returned to parser. */ ]]> Differences from ISO 8879

This grammar assumes the reference concrete syntax; if an alternate concrete syntax is used, some literal strings given in the DTD and document-instance grammars would need to be replaced accordingly.

White space, entity reference, entity end, and comments within markup declarations are assumed to be handled by the lexical scanner and are omitted from this grammar. This shortens and simplifies the grammar somewhat.

The grammar is written as a Backus-Naur-Form (BNF) grammar rather than a regular-right-part grammar; some additional constructs have thus been introduced to deal with repeating and optional items in the original grammar. Non-terminals optional in the original may be required here, and vice versa, depending on how the optionality of a construct has been expressed; in no case does such a change actually affect the set of strings accepted by the grammar.

Some constructs are omitted entirely because they do not occur in the subset of SGML prescribed for use in the TEI Interchange Format: link type declaration short reference set ranked elements and ranked groups data tag group minimized start-tags formal identifiers

Finally, the recognition and expansion of entity references and the handling of marked sections, CDATA and RCDATA elements, and CDATA, SDATA, or NDATA entities have been ignored in the current version. Entity references are assumed to be handled by the lexical scanner, though in a fully conformant SGML parser they are in part dependent on the state of the syntactic parser. CDATA, RCDATA, SDATA, and NDATA elements or entities, like marked sections, are assumed either not to occur or to be handled by the lexical scanner.