The Name-AttValue pairs are referred to as the attribute specifications of the element.

If the declaration is neither #REQUIRED nor #IMPLIED, then the AttValue value contains the declared default value; the #FIXED keyword states that the attribute must always have the default value. If a default value is declared, when an XML processor encounters an omitted attribute, it behaves as though the attribute is present with the declared default value.

Attribute-list declarations specify the name, data type, and default value (if any) of each attribute associated with a given element type.

The name in each pair is referred to as the attribute name.

The content of the AttValue (the text between the ' or " delimiters).

May occur anywhere character data may occur; used to escape blocks of text containing characters that would otherwise be recognized as markup.

An atomic unit of text as specified by ISO/IEC 10646. Legal characters are tab, carriage return, line feed, and the legal graphic characters of Unicode and ISO/IEC 10646. The versions of these standards were current at the time of this writing. New characters may be added to these standards by amendments or new editions. Consequently, XML processors must accept any character in the range specified for Char. The use of compatibility characters is discouraged.

All text that is not markup constitutes the character data of the document.

Refers to a specific character in the ISO/IEC 10646 character set—for example, one not directly accessible from available input devices.

Comments may appear anywhere in a document outside other markup; in addition, they may appear within the Document Type Declaration at places allowed by the grammar. They are not part of the document’s character data; an XML processor may, but need not, make it possible for an application to retrieve the text of comments. For compatibility, the string must not occur within comments.

Portions of the Document Type Declaration external subset, which are included in, or excluded from, the logical structure of the DTD, based on the keyword that governs them.

The text between the start tag and end tag.

In this case, the constraint includes a content model, a simple grammar governing the allowed types of the child elements and the order in which they may appear.

Serves as the root of the entity tree and as a starting point for an XML processor.

The XML Document Type Declaration contains or points to markup declarations that provide a grammar for a class of documents. This grammar is known as a Document Type Definition (DTD). The Document Type Declaration can point to an external subset (a special kind of external entity) containing markup declarations, can contain the markup declarations directly in an internal subset, or can do both. The DTD for a document consists of both subsets taken together.

Each XML document contains one or more elements, the boundaries of which are either delimited by start tags and end tags, or for empty elements, by an empty-element tag. Each element has a type, identified by name, which is sometimes called its generic identifier (GI), and may have a set of attribute specifications.

An element type has element content when elements of that type must contain only child elements (no character data), optionally separated by whitespace (characters matching the nonterminal S).

An element with no content.

An empty-element tag takes a special form: <tagName/>.

The end of every element that begins with a start tag must be marked by an end tag containing a name that echoes the element’s type, as given in the start tag.

An XML document may consist of one or many storage units. These are called entities; all have content and all (except for the document entity and the external DTD subset) are identified by entity name.

Refers to the content of a named entity.

Enumerated attributes can take one of a list of values provided in the declaration.

A violation of the rules of the XML specification; results are undefined. Conforming software may detect and report an error and may recover from it.

Entity and character references can both be used to escape the left-angle bracket, ampersand, and other delimiters. A set of general entities ( amp, lt, gt, apos, quot) is specified for this purpose. Numeric character references may also be used; they are expanded immediately when recognized and must be treated as character data, so the numeric character references #60; and & may be used to escape < and & when they occur in character data.

If the entity is not internal, it is an external entity.

Defined as a markup declaration occurring in the external subset or in a parameter entity (external or internal—the latter being included because nonvalidating processors are not required to read them).

An error that a conforming XML processor must detect and report to the application. After encountering a fatal error, the processor may continue processing the data to search for further errors and may report such errors to the application. In order to support correction of errors, the processor may make unprocessed data from the document (with intermingled character data and markup) available to the application. Once a fatal error is detected, however, the processor must not continue normal processing (i.e., it must not continue to pass character data and information about the document’s logical structure to the application in the normal way).

Entities for use within the document content. In this specification, general entities are sometimes referred to with the unqualified term entity, if this leads to no ambiguity.

References to parsed general entities use ampersands (&) and semicolons (;) as delimiters.

An entity is included when its replacement text is retrieved and processed in place of the reference itself, as though it is part of the document at the location the reference is recognized.

If the entity definition is an EntityValue, the defined entity is called an internal entity. There is no separate physical storage object, and the content of the entity is given in the declaration.

The quoted string actually present in the entity declaration, corresponding to the nonterminal Entity Value.

Markup takes the form of start tags, end tags, empty-element tags, entity references, character references, comments, CDATA section delimiters, Document Type Declarations, processing instructions, XML declarations, text declarations, and any whitespace that is at the top level of the document entity (that is, outside the document element and not inside any other markup).

An element type declaration, an attribute-list declaration, an entity declaration, or a notation declaration.

An element type has mixed content when elements of that type may contain character data, optionally interspersed with child elements.

A token beginning with a letter or one of a few punctuation characters, and continuing with letters, digits, hyphens, underscores, colons, or full stops. Together, these are known as name characters.

Identifies by name the format of unparsed entities, the format of elements that bear a notation attribute, or the application to which a processing instruction is addressed.

Provide a name for the notation, for use in entity and attribute-list declarations and in attribute specifications, and an external identifier for the notation, which may allow an XML processor or its client application to locate a helper application capable of processing data in the given notation.

Parsed entities for use within the DTD.

Parameter-entity references use percent-signs (%) and semicolons (;) as delimiters.

For each nonroot element C in the document, there is one other element P in the document, such that C is in the content of P, but is not in the content of any other element that is in the content of P. P is referred to as the parent of C, and C as a child of P.

While these are not required to check the document for validity, they are required to process all the declarations they read in the internal DTD subset and in any parameter entity that they read, up to the first reference to a parameter entity that they do not read. That is, they must use the information in those declarations to normalize attribute values, include the replacement text of internal entities, and supply default attribute values.

Processing instructions (PIs) allow documents to contain instructions for applications.

In addition to a system identifier, an external identifier may include a public identifier.

The content of the entity, after replacement of character references and parameter-entity references.

There is exactly one element, called the root or document element, of which no part appears in the content of any other element.

Marks the beginning of every nonempty XML element.

The SystemLiteral is called the entity’s system identifier. It is a URI reference (as defined in IETF RFC 2396 and updated by IETF RFC 2732), meant to be dereferenced to obtain input for the XML processor to construct the entity’s replacement text.

A parsed entity contains text (a sequence of characters), which may represent markup or character data.

A parsed entity’s contents are referred to as its replacement text; this text is considered an integral part of the document.

An unparsed entity is a resource whose contents may or may not be text, and if text, may be other than XML. Each unparsed entity has an associated notation, identified by name. Beyond the requirement that an XML processor make the identifiers for the entity and notation available to the application, XML places no constraints on the contents of unparsed entities.

An XML document is valid if it has an associated Document Type Declaration and if the document complies with the constraints expressed in it.

A rule that applies to all valid XML documents. Violations of validity constraints are errors; they must, at user option, be reported by validating XML processors.

Must, at user option, report violations of the constraints expressed by the declarations in the DTD, and failures to fulfill the validity constraints given in this specification.

A textual object is a well-formed XML document if:

1. Taken as whole, it matches the production labeled “document.”

2. It meets all the well-formedness constraints given in the specification.

3. Each of the parsed entities referenced directly or indirectly within the document is well-formed.

A rule that applies to all well-formed XML documents. Violations of well-formedness constraints are fatal errors.

XML documents should begin with an XML declaration that specifies the version of XML being used.

A data object is an XML document if it is well-formed, as defined in this specification. In addition, a well-formed XML document may be valid if it meets certain further constraints.

A software module used to read XML documents and provide access to their content and structure.