A type of element or complex datatype that cannot be used directly in the instance documents. An abstract element must be substituted and is usually the head of a substitution group. An abstract complex type may be used to define content models, in which case the type will have to be substituted in the instance documents using xsi:type. There is no feature to define simple types as abstract (even though the predefined type xs:NOTATION could be considered abstract).


In a regular expression, an atom expresses a condition on a substring. Atoms may be followed by a quantifier defining the expected number of the atom’s occurrences. The atom, with its optional number of occurrences, constitutes a “piece.” An atom may be a character, a wildcard, a special character, a character class, or a regular expression.

atomic type

A simple type that is not derived by list or union from another simple type.


Pieces of information attached to an element and defined in its start tag. Considered child nodes by the XPath data model, and considered property nodes by the DOM, attributes are “information items” to the XML Infoset.

attribute groups

Containers that allow you to define, reference, and redefine groups of attributes.


base type

The datatype that is used as the starting point to define a new datatype by derivation by restriction or extension.

Berners-Lee, Tim

Inventor of HTML and HTTP, and Director of the W3C; he is considered the father of the World Wide Web (see ...

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