ldf.xsd

<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:ldf="http://planet-sl.org/ldf" xmlns:bgf="http://planet-sl.org/bgf" xmlns:xhtml="http://www.w3.org/1999/xhtml" targetNamespace="http://planet-sl.org/ldf">
	<xsd:import namespace="http://planet-sl.org/bgf" schemaLocation="bgf.xsd"/>
	<xsd:import namespace="http://www.w3.org/1998/Math/MathML" schemaLocation="fakemathml.xsd"/>
<!-- info -->
	<xsd:annotation>
		<xsd:documentation>
      Language Document Format
    </xsd:documentation>
		<xsd:documentation>
      This is basically a metamodel for language documents or documentations.

      Sample program tags:
      - External reference (with XPath-like subprogram selection)
      - Verbatim text + claim about corresponding grammar and nonterminal (and perhaps version)
      - Generation request for given grammar and nonterminal (and perhaps version, more control)
      - Sample suite extraction request (what are the constraints on the requested sample?)
    </xsd:documentation>
	</xsd:annotation>
<!-- elements -->
	<xsd:element name="document">
		<xsd:annotation>
			<xsd:documentation>
			  A document is essentially a sequence of several parts, such as title page, front matter,
			  lexical and syntax sections, placeholders for generated content and various lists.
			</xsd:documentation>
		</xsd:annotation>
		<xsd:complexType>
			<xsd:sequence>
				<xsd:element ref="ldf:title-page"/>
				<xsd:element name="content">
					<xsd:complexType>
						<xsd:sequence>
							<xsd:element ref="ldf:part" maxOccurs="unbounded"/>
						</xsd:sequence>
					</xsd:complexType>
				</xsd:element>
			</xsd:sequence>
		</xsd:complexType>
	</xsd:element>
	<xsd:element name="title-page">
		<xsd:complexType>
			<xsd:annotation>
				<xsd:documentation>
        The ``title page'' can in reality be rendered as several pages, but it contains the basic
        information that helps to identify this particular language definition and to distinguish
        it from similar documents. In our experience, language standards are either marked as
        organisation-created or person-authored ones. In the former case, the document must contain
        the name of the organisation and the standard reference number within it (e.g, ISO 10279).
        In the latter case, one or more authors are specified. It is also possible to mark some sections
        as having been authored by a specific set of authors, but the ones defined here are the principal
        authors that identify the specific standard.
      </xsd:documentation>
				<xsd:documentation>
        The ``topic'' of the language document is its pure textual title without the reference number
        and status: e.g., ``Programming Language REXX'',
        ``Information technology --- Programming languages --- Full BASIC'', etc.
		Either version or edition follows.
      </xsd:documentation>
			</xsd:annotation>
			<xsd:sequence>
				<xsd:sequence minOccurs="0">
					<xsd:element ref="ldf:body"/>
					<xsd:element name="number" type="xsd:string"/>
<!-- not always int, can be "38472:1999(E)" etc -->
				</xsd:sequence>
				<xsd:element ref="ldf:metainfo"/>
				<xsd:element ref="ldf:status"/>
				<xsd:choice>
					<xsd:element name="version" type="xsd:string" default="1.0"/>
					<xsd:element name="edition" type="xsd:string"/>
				</xsd:choice>
				<xsd:element ref="ldf:previous" minOccurs="0" maxOccurs="unbounded"/>
				<xsd:element name="date" type="xsd:string"/>
<!-- xsd:date -->
			</xsd:sequence>
		</xsd:complexType>
	</xsd:element>
	<xsd:element name="body">
		<xsd:simpleType>
			<xsd:restriction base="xsd:token">
				<xsd:enumeration value="ansi"/>
				<xsd:enumeration value="ecma"/>
				<xsd:enumeration value="ieee"/>
				<xsd:enumeration value="iec"/>
				<xsd:enumeration value="iso"/>
				<xsd:enumeration value="iso/iet"/>
				<xsd:enumeration value="itu"/>
				<xsd:enumeration value="iec"/>
				<xsd:enumeration value="ietf"/>
				<xsd:enumeration value="oasis"/>
				<xsd:enumeration value="omg"/>
				<xsd:enumeration value="wsa"/>
				<xsd:enumeration value="w3c"/>
			</xsd:restriction>
		</xsd:simpleType>
	</xsd:element>
	<xsd:element name="status">
		<xsd:annotation>
			<xsd:documentation>
        According to W3C Process Document, each viable specification goes through the stages
        of Working Draft (WD), Candidate Recommendation (CR), Proposed Recommendation (PR),
        W3C Recommendation (REC), with possible continuation to Proposed Edited Recommendation
        and decline to Rescinded Recommendation. There has also been a ``Note'' status in the past
        for internal drafts.
      </xsd:documentation>
			<xsd:documentation>
        IEEE uses different publication types, they are:
        Changed Designation,
        Collection,
        New Standard Project,
        Modified New Project,
        Modified Revision Project,
        Revision Project,
        Adoption in Progress,
        Approved Publication of IEEE,
        International Publication,
        Trial Use,
        Amendment,
        Corrigenda of Standard,
        Superseded,
        Withdrawn (IEEE Status Report).
      </xsd:documentation>
			<xsd:documentation>
        ISO/IEC operates with the following standard ratification stages:
        Approved Work Item (AWI),
        Working Draft (WD), Committee Draft (CD),
        Committee Draft Technical Report (CD TR),
        Committee Draft Technical Specification (CD TS),
        Committee Draft for Vote (CDV, only for IEC),
        Draft International Standard (DIS),
        Final Committee Draft (FCD, only for JTC1),
        Draft Technical Report (DTR),
        Draft Technical Specification (DTS),
        Final Draft International Standard (FDIS),
        International Standard (ISO),
        Technical Report (ISO TR),
        Technical Specification (ISO TS).
      </xsd:documentation>
			<xsd:documentation>
        Some standardisation bodies like ANSI or ECMA do not have a long list of stages, the
        standard there is just either approved or not. Of course, it still can be revised,
        reaffirmed, withdrawn or be put into a category of technical reports.
      </xsd:documentation>
			<xsd:documentation>
        We summarise these and possibly other sets of statuses by the following enumeration.
        Conceptually it provides functionality for the same categories, but the concrete
        wording may vary (i.e., ``errata'' vs ``corrigenda'', ``obsolete'' vs ``rescinded'').
        If necessary, the schema can be extended with more standard publication types
        or even adapted to fit completely in some specific standardisation body classification.
      </xsd:documentation>
		</xsd:annotation>
		<xsd:simpleType>
			<xsd:restriction base="xsd:token">
				<xsd:enumeration value="unknown"/>
				<xsd:enumeration value="draft"/>
<!-- working draft, committee draft -->
				<xsd:enumeration value="candidate"/>
				<xsd:enumeration value="proposed"/>
				<xsd:enumeration value="approved"/>
<!-- recommendation, international standard -->
				<xsd:enumeration value="revised"/>
				<xsd:enumeration value="obsolete"/>
				<xsd:enumeration value="withdrawn"/>
				<xsd:enumeration value="collection"/>
				<xsd:enumeration value="trial"/>
				<xsd:enumeration value="errata"/>
				<xsd:enumeration value="report"/>
			</xsd:restriction>
		</xsd:simpleType>
	</xsd:element>
	<xsd:element name="previous">
		<xsd:annotation>
			<xsd:documentation>
				Previous versions of the same standard.
	      </xsd:documentation>
		</xsd:annotation>
		<xsd:complexType>
			<xsd:sequence>
				<xsd:element name="title" type="xsd:string"/>
				<xsd:choice minOccurs="0">
					<xsd:element name="version" type="xsd:string"/>
					<xsd:element name="edition" type="xsd:string"/>
				</xsd:choice>
				<xsd:element name="uri" type="xsd:anyURI" minOccurs="0"/>
			</xsd:sequence>
		</xsd:complexType>
	</xsd:element>
	<xsd:element name="part">
		<xsd:annotation>
			<xsd:documentation>
				Document part.
	      </xsd:documentation>
		</xsd:annotation>
		<xsd:complexType>
			<xsd:sequence>
				<xsd:element name="role" type="ldf:part-role"/>
				<xsd:element ref="ldf:metainfo"/>
				<xsd:element name="content">
					<xsd:complexType>
						<xsd:sequence>
							<xsd:group ref="ldf:section" maxOccurs="unbounded"/>
						</xsd:sequence>
					</xsd:complexType>
				</xsd:element>
			</xsd:sequence>
		</xsd:complexType>
	</xsd:element>
	<xsd:element name="metainfo">
		<xsd:complexType>
			<xsd:sequence>
				<xsd:element name="id" type="xsd:ID" minOccurs="0"/>
				<xsd:element name="title" type="xsd:string" minOccurs="0"/>
				<xsd:element name="author" type="xsd:string" minOccurs="0" maxOccurs="unbounded"/>
			</xsd:sequence>
		</xsd:complexType>
	</xsd:element>
	<xsd:simpleType name="part-role">
		<xsd:restriction base="xsd:token">
			<xsd:enumeration value="front-matter"/>
			<xsd:enumeration value="core-part"/>
			<xsd:enumeration value="back-matter"/>
			<xsd:enumeration value="annex"/>
		</xsd:restriction>
	</xsd:simpleType>
	<xsd:group name="section">
		<xsd:choice>
			<xsd:element ref="ldf:placeholder">
				<xsd:annotation>
					<xsd:documentation>
		            Placeholders are used to designate places where generated content
		            should be inserted.
		          </xsd:documentation>
				</xsd:annotation>
			</xsd:element>
			<xsd:element ref="ldf:simple-section"/>
			<xsd:element ref="ldf:lexical-section"/>
			<xsd:element ref="ldf:structured-section"/>
			<xsd:element ref="ldf:composite-section"/>
			<xsd:element ref="ldf:list-section"/>
		</xsd:choice>
	</xsd:group>
	<xsd:element name="composite-section">
		<xsd:complexType>
			<xsd:sequence>
				<xsd:group ref="ldf:section" maxOccurs="unbounded"/>
			</xsd:sequence>
		</xsd:complexType>
	</xsd:element>
	<xsd:element name="placeholder">
		<xsd:simpleType>
			<xsd:annotation>
				<xsd:documentation>
        Entities such as table of contents can be generated by the infrastructure automatically,
        ensuring internal consistency and coherence. However, the language documentation creators
        should be able to specify the places where such data needs to be inserted.
      </xsd:documentation>
			</xsd:annotation>
			<xsd:restriction base="xsd:token">
				<xsd:enumeration value="index"/>
				<xsd:enumeration value="full-grammar"/>
				<xsd:enumeration value="list-of-tables"/>
				<xsd:enumeration value="list-of-authors"/>
				<xsd:enumeration value="list-of-contents"/>
				<xsd:enumeration value="list-of-references"/>
			</xsd:restriction>
		</xsd:simpleType>
	</xsd:element>
	<xsd:element name="simple-section">
		<xsd:complexType>
			<xsd:annotation>
				<xsd:documentation>
	        Innermost sections do not have to belong to a certain pre-defined type
	        (like ``synopsis'' or ``design goals''), but they can have a title
	        and a possible list of authors which contributed directly to this section.
	      </xsd:documentation>
			</xsd:annotation>
			<xsd:sequence>
				<xsd:element name="role" type="ldf:simple-section-role"/>
				<xsd:element ref="ldf:metainfo"/>
				<xsd:element name="content" type="ldf:textual-content"/>
			</xsd:sequence>
		</xsd:complexType>
	</xsd:element>
	<xsd:simpleType name="simple-section-role">
		<xsd:restriction base="xsd:token">
			<xsd:enumeration value="abstract">
				<xsd:annotation>
					<xsd:documentation>
					Just like scientific papers, some of language documents can have a very short
					abstract that summarises their goals and covered topics in one or two
					sentences.
		          </xsd:documentation>
				</xsd:annotation>
			</xsd:enumeration>
			<xsd:enumeration value="foreword">
				<xsd:annotation>
					<xsd:documentation>
		            Whatever the authors deem to be important enough to be put on one of the first
		            pages. For example, in C\# specifications Foreword is about the differences brought
		            to the language by the current standard, while in the Scheme specification
		            Foreword discusses programming languages design and demonstrates its principles
		            applied to the forthcoming document.
		          </xsd:documentation>
					<xsd:documentation>
		            Technically speaking, Foreword is not a part of the specification. Instead, it
		            precedes the specification and introduces it by putting in the proper context.
		          </xsd:documentation>
				</xsd:annotation>
			</xsd:enumeration>
			<xsd:enumeration value="conformance">
				<xsd:annotation>
					<xsd:documentation>
		            Conformance (compliance) section defines several levels of compliance by
		            explaining what is a conforming program and a conforming
		            implementation with respect to this standard.
		          </xsd:documentation>
					<xsd:documentation>
		            Definitions for meta-terms like "shall" and "should"
		            and their relation to the compliance issue explained above.
		          </xsd:documentation>
				</xsd:annotation>
			</xsd:enumeration>
			<xsd:enumeration value="compatibility">
				<xsd:annotation>
					<xsd:documentation>
		            While conformance/compliance define how external artifacts should
		            conform to this standard, this section defines how this standard
		            complies with previously existing ones.
		          </xsd:documentation>
				</xsd:annotation>
			</xsd:enumeration>
			<xsd:enumeration value="design-goals">
				<xsd:annotation>
					<xsd:documentation>
		            The goals of language design are sometimes encountered being explicitly
		            stated in the language document in one of the informative sections
		            of the front matter part.
		          </xsd:documentation>
					<xsd:documentation>
		            For example:
		            "C\# is intended to be a simple, modern, general-purpose, object-oriented
		            programming language."
		            (from ECMA 334 3rd edition, page xvii)
		          </xsd:documentation>
				</xsd:annotation>
			</xsd:enumeration>
			<xsd:enumeration value="document-structure">
				<xsd:annotation>
					<xsd:documentation>
		            This section informally describes how the document is organised, divided
		            into parts and chapters. Sometimes it explicitly states which sections are
		            normative and which are informative.
		          </xsd:documentation>
				</xsd:annotation>
			</xsd:enumeration>
			<xsd:enumeration value="foreword">
	        </xsd:enumeration>
			<xsd:enumeration value="normative-references">
				<xsd:annotation>
					<xsd:documentation>
		            Formally lined up references to all other standards that are used or referenced to
		            from within the document.
		          </xsd:documentation>
				</xsd:annotation>
			</xsd:enumeration>
			<xsd:enumeration value="notation">
				<xsd:annotation>
					<xsd:documentation>
		            Notation section defines grammar definition formalism used in the document:
		            mostly it is about the EBNF dialect.
		          </xsd:documentation>
				</xsd:annotation>
			</xsd:enumeration>
			<xsd:enumeration value="scope">
				<xsd:annotation>
					<xsd:documentation>
		            Scope section explains the context for the language document.
		          </xsd:documentation>
				</xsd:annotation>
			</xsd:enumeration>
			<xsd:enumeration value="what-is-new">
				<xsd:annotation>
					<xsd:documentation>
		            A list of changes brought to the language by the current specification
		            replacing the previous one.
		          </xsd:documentation>
				</xsd:annotation>
			</xsd:enumeration>
		</xsd:restriction>
	</xsd:simpleType>
	<xsd:element name="lexical-section">
		<xsd:complexType>
			<xsd:annotation>
				<xsd:documentation>
	        Sections describing lexical structure tend to be shorter, less structured inside,
	        and very limited in scope: there is usually one lexical section dedicated to whitespace,
			one lexical section about tokens, one about literals, one about comments, etc.
	      </xsd:documentation>
				<xsd:documentation>
	        See the section on grammar notation for more details about how broad even the smallest
	        aspects (e.g., about line continuations) can vary.
	      </xsd:documentation>
			</xsd:annotation>
			<xsd:sequence>
				<xsd:element name="role" type="ldf:lexical-section-role"/>
				<xsd:element ref="ldf:metainfo"/>
				<xsd:element name="content" type="ldf:textual-content"/>
			</xsd:sequence>
		</xsd:complexType>
	</xsd:element>
	<xsd:simpleType name="lexical-section-role">
		<xsd:restriction base="xsd:token">
			<xsd:enumeration value="lexical-issue">
			</xsd:enumeration>
			<xsd:enumeration value="line-continuations">
			</xsd:enumeration>
			<xsd:enumeration value="literals">
			</xsd:enumeration>
			<xsd:enumeration value="preprocessor">
			</xsd:enumeration>
			<xsd:enumeration value="tokens">
			</xsd:enumeration>
			<xsd:enumeration value="whitespace">
			</xsd:enumeration>
		</xsd:restriction>
	</xsd:simpleType>
	<xsd:element name="list-section">
		<xsd:complexType>
			<xsd:sequence>
				<xsd:element name="role" type="ldf:list-section-role"/>
				<xsd:element ref="ldf:metainfo"/>
				<xsd:element name="content">
					<xsd:complexType>
						<xsd:sequence>
							<xsd:element ref="ldf:term" maxOccurs="unbounded"/>
						</xsd:sequence>
					</xsd:complexType>
				</xsd:element>
			</xsd:sequence>
		</xsd:complexType>
	</xsd:element>
	<xsd:simpleType name="list-section-role">
		<xsd:restriction base="xsd:token">
			<xsd:enumeration value="abbreviations">
			</xsd:enumeration>
			<xsd:enumeration value="definitions">
			</xsd:enumeration>
			<xsd:enumeration value="language-overview">
			</xsd:enumeration>
			<xsd:enumeration value="normative-references">
			</xsd:enumeration>
		</xsd:restriction>
	</xsd:simpleType>
	<xsd:element name="term">
		<xsd:complexType>
			<xsd:sequence>
				<xsd:element name="name" type="xsd:string"/>
				<xsd:element name="definition" type="ldf:textual-content"/>
			</xsd:sequence>
		</xsd:complexType>
	</xsd:element>
	<xsd:element name="structured-section">
		<xsd:complexType>
			<xsd:sequence>
				<xsd:element ref="ldf:metainfo"/>
<!-- title here should be required -->
				<xsd:element name="content">
					<xsd:complexType>
						<xsd:sequence>
							<xsd:group ref="ldf:structured-section-element" maxOccurs="unbounded"/>
						</xsd:sequence>
					</xsd:complexType>
				</xsd:element>
			</xsd:sequence>
		</xsd:complexType>
	</xsd:element>
	<xsd:group name="structured-section-element">
		<xsd:choice>
			<xsd:element name="subtopic">
				<xsd:annotation>
					<xsd:documentation>
		            In big documents it is not uncommon to find one topic divided into
		            several subtopics, each one dedicated to a separate issue and each one
		            structured in the same way its parent section is.
		            DSLs and 4GLs specification authors often find it easier to lay out
		            different clauses of one language construct in different sections.
		            When the language has a lot of parametrised constructs, it makes sense
		            to dedicate a special subsection for each field.
		            Parameters, types, methods, operations, participants---whatever categories
		            inspire these subtopics, each of them is a fully structured section in itself.
		          </xsd:documentation>
				</xsd:annotation>
				<xsd:complexType>
					<xsd:sequence>
						<xsd:element ref="ldf:structured-section"/>
					</xsd:sequence>
				</xsd:complexType>
			</xsd:element>
			<xsd:element name="references" type="ldf:list">
				<xsd:annotation>
					<xsd:documentation>
		            Even hardbound standards contain hypertext-like elements.
					One of them is attaching a list of links
		            and backlinks to every section---that way, one can easily
		            find any related language constructs when learning the
		            language or debugging a particular feature.
		          </xsd:documentation>
				</xsd:annotation>
			</xsd:element>
			<xsd:element ref="ldf:placeholder">
				<xsd:annotation>
					<xsd:documentation>
		            Some subsections can be generated, especially those that consist
		            of structured content that is possible to derive automatically
		            from the information stored in or collected from other sections.
		          </xsd:documentation>
				</xsd:annotation>
			</xsd:element>
			<xsd:element name="value">
				<xsd:annotation>
					<xsd:documentation>
		            A singled named value can be bound to a language document section: it can be
		            a type of a parameter that is being described here, or an alternative name,
		            or a superclass, or anything else that is atomic and non-structured.
		          </xsd:documentation>
				</xsd:annotation>
				<xsd:complexType>
					<xsd:sequence>
						<xsd:element name="key" type="xsd:string"/>
						<xsd:element name="data" type="xsd:string"/>
					</xsd:sequence>
				</xsd:complexType>
			</xsd:element>
			<xsd:sequence>
				<xsd:choice minOccurs="0">
					<xsd:element ref="ldf:normative-role">
						<xsd:annotation>
							<xsd:documentation>
							  Normative sections are obligatory and usually contain strict content
							  that needs to be implemented by compiler developers or satisfied
							  by language end users in order to comply to this standard.
							</xsd:documentation>
							<xsd:documentation>
							  For instance, if a section with a grammar production is marked as
							  normative, this production must hold for the implemented language.
							</xsd:documentation>
						</xsd:annotation>
					</xsd:element>
					<xsd:element ref="ldf:informative-role">
						<xsd:annotation>
							<xsd:documentation>
								Informative sections are supplementary and provide some useful information
								that can be omitted or overridden if deemed appropriately.
							</xsd:documentation>
							<xsd:documentation>
							  For instance, if all sections with code samples are marked as informative,
							  we cannot rely on the set of examples extracted from the standard to be
							  the test set for the language. Apparently, we can still run some analyses
							  on the basis of this, but it is not legitimate to make any conclusions
							  about standard inconsistencies based on the informative sections, nor can
							  they be legitimately be used to resolve inner conflicts of the documentation.
							</xsd:documentation>
						</xsd:annotation>
					</xsd:element>
				</xsd:choice>
				<xsd:element ref="ldf:simple-section"/>
			</xsd:sequence>
		</xsd:choice>
	</xsd:group>
	<xsd:element name="normative-role">
		<xsd:simpleType>
			<xsd:annotation>
				<xsd:documentation>
	        Normative sections form the core of the language standard: for each core section they belong to,
	        they define the purpose of the language construct, provide a description, a syntax definition,
	        list use constraints and other semantic details, etc.
	      </xsd:documentation>
			</xsd:annotation>
			<xsd:restriction base="xsd:token">
				<xsd:enumeration value="synopsis">
					<xsd:annotation>
						<xsd:documentation>
		            A separate subsection named ``purpose'' is only encountered in some 4GL
		            language manuals (e.g., JCL). However, it is quite common for the first
		            paragraph of any new section of any language document to briefly introduce
		            the purpose of the language construct that is about to be described.
		          </xsd:documentation>
					</xsd:annotation>
				</xsd:enumeration>
				<xsd:enumeration value="description">
					<xsd:annotation>
						<xsd:documentation>
		            Description is the core of the parent section, containing the main details about the
		            defined topic, information about its usage, motivation behind its design.
		          </xsd:documentation>
					</xsd:annotation>
				</xsd:enumeration>
				<xsd:enumeration value="syntax">
					<xsd:annotation>
						<xsd:documentation>
		            Syntax sections consist of one or more BGF productions, possibly complemented by textual descriptions.
		          </xsd:documentation>
					</xsd:annotation>
				</xsd:enumeration>
				<xsd:enumeration value="constraints">
					<xsd:annotation>
						<xsd:documentation>
		            This section can list requirements needed for using a specific language construct,
		            applicability constraints and other restrictions.
		          </xsd:documentation>
					</xsd:annotation>
				</xsd:enumeration>
				<xsd:enumeration value="relationship">
					<xsd:annotation>
						<xsd:documentation>
		            Related language constructs can be named and referenced here.
		            It is not a simple list of references, but rather a comprehensive
		            overview on the kind of consequences other parts of the language
		            can bear if this one is used.
		          </xsd:documentation>
					</xsd:annotation>
				</xsd:enumeration>
				<xsd:enumeration value="semantics">
					<xsd:annotation>
						<xsd:documentation>
		            A section on semantics explains in plain English, if no other specific formalism
		            is used, how exactly the language construct works, what happens inside the system when
		            it is utilised. It also describes the context in which the introduced language construct
		            can be encountered and in which it should or should not be used.
		          </xsd:documentation>
					</xsd:annotation>
				</xsd:enumeration>
				<xsd:enumeration value="default">
					<xsd:annotation>
						<xsd:documentation>
		            It is quite common in the sections that describe an optional parameter
		            to tell the reader what will happen in the case nothing was specified.
		            ``There is no default'' can be as valid a definition as a real default value.
		          </xsd:documentation>
					</xsd:annotation>
				</xsd:enumeration>
			</xsd:restriction>
		</xsd:simpleType>
	</xsd:element>
	<xsd:element name="informative-role">
		<xsd:simpleType>
			<xsd:annotation>
				<xsd:documentation>
		        Unlike normative sections that impose some conformance constraints that need
		        to be satisfied by a language processor to claim compatibility with the standard,
		        the informative sections are only presented to provide some additional information
		        to the reader.
		      </xsd:documentation>
			</xsd:annotation>
			<xsd:restriction base="xsd:token">
				<xsd:enumeration value="example">
					<xsd:annotation>
						<xsd:documentation>
			            A subsection with an example can contain a code sample as well
			            as some accompanying text.
			          </xsd:documentation>
					</xsd:annotation>
				</xsd:enumeration>
				<xsd:enumeration value="rationale">
					<xsd:annotation>
						<xsd:documentation>
			            A rationale or a note usually lists some narrow places of
			            non-obvious usage, implementation details, incompatibility issues,
			            coding standards, common programming practices, etc. It is a
			            subsection of secondary importance, contributing some information
			            on a minor point that can still be interesting and useful for some
			            readers. Notes usually tell the readers how to use certain language
			            constructs or tell compiler vendors how to implement them.
			          </xsd:documentation>
					</xsd:annotation>
				</xsd:enumeration>
				<xsd:enumeration value="update">
					<xsd:annotation>
						<xsd:documentation>
			            It is quite uncommon practice, but some standardisation bodies really
			            put the information about language evolution directly into each section
			            that changed since the last public version of the language document.
			          </xsd:documentation>
						<xsd:documentation>
			            If this is done consistently and carefully, it is possible to generate
			            the global ``What's new'' section automatically.
			          </xsd:documentation>
					</xsd:annotation>
				</xsd:enumeration>
			</xsd:restriction>
		</xsd:simpleType>
	</xsd:element>
	<xsd:complexType name="textual-content">
		<xsd:sequence>
			<xsd:group ref="ldf:text-element" maxOccurs="unbounded"/>
		</xsd:sequence>
	</xsd:complexType>
	<xsd:group name="text-element">
		<xsd:choice>
			<xsd:element name="empty" nillable="true">
				<xsd:complexType/>
			</xsd:element>
			<xsd:element name="code" type="xsd:string"/>
<!-- inline sample -->
			<xsd:element name="text" type="ldf:mixed-type"/>
			<xsd:element ref="ldf:figure"/>
			<xsd:element ref="ldf:table"/>
			<xsd:element name="list" type="ldf:list"/>
			<xsd:element name="formula">
				<xsd:complexType>
					<xsd:sequence maxOccurs="unbounded">
						<xsd:any namespace="http://www.w3.org/1998/Math/MathML"/>
					</xsd:sequence>
				</xsd:complexType>
			</xsd:element>
<!--<xsd:element name="sample">
        <xsd:complexType>
          <xsd:simpleContent>
            <xsd:extension base="xsd:string">
              <xsd:attribute name="src" type="xsd:string"/>
            </xsd:extension>
          </xsd:simpleContent>
        </xsd:complexType>
      </xsd:element>-->
			<xsd:element name="sample">
				<xsd:complexType mixed="true">
					<xsd:sequence minOccurs="0" maxOccurs="unbounded">
						<xsd:any namespace="http://www.w3.org/1999/xhtml" processContents="lax"/>
					</xsd:sequence>
					<xsd:attribute name="source" type="xsd:string"/>
				</xsd:complexType>
			</xsd:element>
			<xsd:element ref="bgf:production"/>
<!-- 	later redo with MathML -->
<!--<xsd:element ref="mml:math" />-->
		</xsd:choice>
	</xsd:group>
	<xsd:element name="figure">
		<xsd:complexType>
			<xsd:annotation>
				<xsd:documentation>
        A figure in LDF can include several presentation variants in different formats.
        Any of them can be chosen by the rendering tool: for example, in our prototype,
        \TeX\ generators prefer PDF figures while HTML generators tend to prefer PNG ones.
      </xsd:documentation>
			</xsd:annotation>
			<xsd:sequence>
				<xsd:element ref="ldf:metainfo"/>
<!-- title => caption; ? => short-caption -->
				<xsd:element name="source" type="ldf:figure-source" maxOccurs="unbounded"/>
			</xsd:sequence>
		</xsd:complexType>
	</xsd:element>
	<xsd:complexType name="figure-source">
		<xsd:sequence>
			<xsd:element name="type" type="ldf:figure-type"/>
			<xsd:choice>
				<xsd:element name="local-file" type="xsd:string"/>
				<xsd:element name="uri" type="xsd:anyURI"/>
			</xsd:choice>
		</xsd:sequence>
	</xsd:complexType>
	<xsd:simpleType name="figure-type">
		<xsd:restriction base="xsd:token">
			<xsd:enumeration value="PDF"/>
			<xsd:enumeration value="PostScript"/>
			<xsd:enumeration value="SVG"/>
			<xsd:enumeration value="PNG"/>
			<xsd:enumeration value="GIF"/>
			<xsd:enumeration value="JPEG"/>
		</xsd:restriction>
	</xsd:simpleType>
	<xsd:element name="table">
		<xsd:complexType>
			<xsd:annotation>
				<xsd:documentation>
        Tables have header rows (optional) and regular rows, with each row filled with table cells.
      </xsd:documentation>
			</xsd:annotation>
			<xsd:sequence>
				<xsd:element name="header" type="ldf:table-row" minOccurs="0" maxOccurs="unbounded"/>
				<xsd:element name="row" type="ldf:table-row" maxOccurs="unbounded"/>
			</xsd:sequence>
		</xsd:complexType>
	</xsd:element>
	<xsd:complexType name="table-row">
		<xsd:sequence>
			<xsd:element name="table-cell" type="ldf:textual-content" maxOccurs="unbounded"/>
		</xsd:sequence>
	</xsd:complexType>
	<xsd:complexType name="list">
		<xsd:annotation>
			<xsd:documentation>
			  A list in LDF is nothing more sophisticated than a sequence of textual items.
			</xsd:documentation>
		</xsd:annotation>
		<xsd:sequence>
			<xsd:element name="item" type="ldf:mixed-type" maxOccurs="unbounded"/>
		</xsd:sequence>
	</xsd:complexType>
	<xsd:complexType name="mixed-type" mixed="true">
		<xsd:annotation>
			<xsd:documentation>
        Any unstructured element of the language document belongs to a so called
        mixed type: i.e., it is plain text with some keywords marked.
      </xsd:documentation>
		</xsd:annotation>
		<xsd:sequence minOccurs="0" maxOccurs="unbounded">
			<xsd:any namespace="http://planet-sl.org/ldf" processContents="lax"/>
		</xsd:sequence>
<!--<xsd:anyAttribute namespace="##other" processContents="lax"/>-->
	</xsd:complexType>
	<xsd:element name="formula">
		<xsd:annotation>
			<xsd:documentation>
        Formulae can be used in language documentation in many ways.
        The internal representation format is MathML which is W3C Recommendation,
        but the external representation can vary, in our case there are two:
        \TeX\ and HTML.
      </xsd:documentation>
		</xsd:annotation>
		<xsd:complexType>
			<xsd:sequence maxOccurs="unbounded">
				<xsd:any namespace="http://www.w3.org/1998/Math/MathML"/>
			</xsd:sequence>
		</xsd:complexType>
	</xsd:element>
	<xsd:element name="keyword" type="xsd:string">
		<xsd:annotation>
			<xsd:documentation>
        Keywords are usually printed in bolder font weight.
        They need to be marked as such for two purposes: for presentation and for meta-information.
        The former goal serves as a basis for typesetting and hyperlinking,
        while the latter allows for correct indexing and searching facilities.
      </xsd:documentation>
		</xsd:annotation>
	</xsd:element>
	<xsd:element name="code" type="xsd:string">
		<xsd:annotation>
			<xsd:documentation>
        Inlined pieces of code are usually printed in a typewriter-like font.
        They are frequently incomplete, mostly nothing more than simple literals,
        and can only be checked to be correct tokens of the language in
        a lexical sense.
      </xsd:documentation>
		</xsd:annotation>
	</xsd:element>
	<xsd:element name="link">
		<xsd:annotation>
			<xsd:documentation>
			  Internal links are pairs of text that will become clickable in hypertext
			  presentation forms or precede the reference itself when this is the only
			  option. The reference points to a section or a subsection of the same
			  document that the link should refer to. If the explicit text is omitted,
			  its default value is the name of the section being referenced.
			</xsd:documentation>
		</xsd:annotation>
		<xsd:complexType>
			<xsd:sequence>
<!--<xsd:element name="text" type="xsd:string"/>-->
				<xsd:element name="text" type="xsd:string" minOccurs="0"/>
				<xsd:choice>
					<xsd:element name="reference" type="xsd:string"/>
<!--IDREF -->
					<xsd:element name="external" type="xsd:anyURI"/>
				</xsd:choice>
			</xsd:sequence>
		</xsd:complexType>
	</xsd:element>
</xsd:schema>