Checking XML Well-Formedness

Well-Formedness Rules

The XML Syntax rules for Well-formed XML are as follows:

• All XML elements must have a closing tag.
• XML tags are case-sensitive.
• All XML elements must be properly nested.
• All XML documents must have a root element.
• Attribute values must always be quoted.
• With XML, whitespace is preserved.

The Namespace-wellformed rules are as follows:

• All element and attribute names contain either zero or one colon.
• No entity names, processing instruction targets, or notation names contain any colons.

The Namespace-valid rules are as follows:

• The xml prefix is by definition bound to the namespace name: http://www.w3.org/XML/1998/namespace. It MAY be declared, but MUST NOT be undeclared or bound to any other namespace name. Other prefixes MUST NOT be bound to this namespace name.
• The xmlns prefix is used only to declare namespace bindings and is by definition bound to the namespace name: http://www.w3.org/2000/xmlns/. It MUST NOT be declared or undeclared. Other prefixes MUST NOT be bound to this namespace name.
• All other prefixes beginning with the three-letter sequence x, m, l, in any case combination, are reserved. This means that users SHOULD NOT use them except as defined by later specifications and processors MUST NOT treat them as fatal errors.
• The namespace prefix (unless it is xml or xmlns) MUST have been declared in a namespace declaration attribute in either the start tag of the element where the prefix is used or in an ancestor element (for example, an element in whose content the prefixed markup occurs). Furthermore, the attribute value in the innermost such declaration MUST NOT be an empty string.

Check for Well-Formedness

To check if a document is Namespace Well-Formed XML, select the Check Well-Formedness (Ctrl + Shift + W (Command + Shift + W on OS X)) action from the Document ⇒ Validate menu or from the Validation drop-down menu on the toolbar.

The selected files in the current project can also be checked for well-formedness with a single action by selecting the Check Well-Formedness action from the Validate submenu when invoking the contextual menu in the Project view.

If any errors are found, the result is displayed in the message panel at the bottom of the editor. Each error is displayed as one record in the result list and is accompanied by an error message. Clicking the record will open the document containing the error and highlight its approximate location.