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