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XML stands for eXtensible Markup Language.
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XML documents are structured, tagged documents composed of elements, attributes, processing instructions, namespace declarations, comments, and text.
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<root></root> |
<root /> |
<root>child data</root> |
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There can be exactly one root element of an XML document. (The document element)
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Elements have a name and may also have children; Child data may be text, elements, attributes, or other types of XML structures.
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Element names are case-sensitive
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Elements must be correctly nested:
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<outer><inner>Content</inner></outer> |
<outer><inner>Content</outer></inner> |
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Element names must start with a letter or underscore. The following characters may contain letters, digits, periods, hyphens, underscores, or colons.
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key='value' |
key="value" |
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Elements can be annotated with attributes. Attributes cannot exist in a serialized document without a parent element.
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Attributes are name/value pairs that are separated by an equals sign, with a value surrounded by matching sing or double quotes.
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The attributes for an element are serialized within the start tag of an element.
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<User login="J.Smith" enrolled="2014-12-14" /> |
<User enrolled="2014-12-14">J.Smith</User> |
<prefix:localname xmlns:prefix="URI" /> |
<tagname xmlns="URI" /> |
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Namespaces resolve ambiguity when tag names collide.
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Namespace declarations appear in an element start tag and are typically mapped to shorter prefix.
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Namespace declarations are scoped to the element they are defined in, and all descendants thereof.
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All elements in an XML document are QNames (qualified names); A QName is a local name with an optional prefix.
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Both the prefix and the local name are NCNames (No-colon names).
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The namespace of an element with a given prefix is the namespace specified by the in-scope namespace declaration for that prefix. (May be overridden)
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The namespace of un-prefixed elements is the default namespace.
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Attribute names are QNames; unprefixed attributes are in no namespace, even if a default namespace is in scope.
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<!-- Commented text --> |
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Comments can contain spaces, text, elements, and line breaks, and can therefore span multiple lines of XML
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You may not use a double hyphen (
--) within a comment itself; therefore, you cannot nest comments |
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&#DecimalUnicodeValue;
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&#xHexadecimalUnicodeValue;
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Character references can only be used for element and attribute content
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<?xml version="1.0"?> |
<?target data?> |
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Only processing instructions and comments may appear before the document lement
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The processing instruction target
xml is reserved |
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No processing instruction may start with the string
xml or any recapitalization thereof |
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There are five predefined entities used in the XML markup which must be escaped in order to appear in XML content
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&
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&
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<
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<
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>
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>
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"
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"
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'
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'
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You may not use (<) or (&) anywhere in your XML document, except to begin a tag or an entity, respectively
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<![CDATA[Almost any content here]]> |
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Use a
CDATA section to include content that you do not want the XML parser to interpret |
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CDATA stands for (unparsed) character data, as opposed to PCDATA (parsed character data)
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You may not nest CDATA sections
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CDATA sections may be used anywhere withing the root element of an XML document
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If you need to include the string
]]> in the CDATA text, and you are not closing the CDATA section, the closing > must be written as > |
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