A Well-Formed XML document is a document that conforms to the XML syntax rules. A Namespace Well-Formed XML document is a document that is XML Well-Formed and is also namespace-wellformed and namespace-valid.
The XML Syntax rules for Well-Formed XML are:
- 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, white space is preserved.
The namespace-wellformed rules are:
- 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:
- The prefix xml is by definition bound to the namespace name http://www.w3.org/XML/1998/namespace. It MAY, but need not, be declared, and MUST NOT be undeclared or bound to any other namespace name. Other prefixes MUST NOT be bound to this namespace name.
- The prefix xmlns 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 (i.e. an element in whose content the prefixed markup occurs). Furthermore, the attribute value in the innermost such declaration MUST NOT be an empty string.
To check if a document is Namespace Well-Formed XML, go to . You can also open the drop-down menu of the 
validate button on the toolbar and
select
Check
Well-Formedness. If any error is found the result is returned to the message
panel. Each error is 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.
A not Well-Formed XML Document
<root><tag></root>When Check Well-Formedness is performed the following error is raised:
The element type "tag" must be terminated by the matching end-tag "</tag>"
To resolve the error, click in the result list record which will locate and highlight the errors approximate position. Identify which start tag is missing an end tag and insert </tag>.
A not namespace-wellformed document
<x::y></x::y>When Check document form is performed the following error is raised:
Element or attribute do not match QName production: QName::=(NCName':')?NCName.
A not namespace-valid document
<x:y></x:y>When Check document form is performed the following error is raised:
The prefix "x" for element "x:y" is not bound.
Also the files contained in the current project and selected with the mouse in the Project view can be checked for
well-formedness with one action available on the popup menu of the Project view : Check
Well-Formedness.
