What does xmlns

Attributes can be qualified but are generally not. They also do not inherit their namespace from the element they are on, as opposed to elements see below. Also, element namespaces are inherited from the parent element. In other words I could equally have written the above XML as. Think of the namespace prefix as a variable with a short name alias for the full namespace URI. I think the biggest confusion is that xml namespace is pointing to some kind of URL that doesn't have any information.

But the truth is that the person who invented below namespace:. This is just a unique identifier. Your message has been sent to W3Schools. W3Schools is optimized for learning and training. Examples might be simplified to improve reading and learning. Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. What is it? Improve this question. Now you would have also got to know that why we get errors in the xml when we use the tags incorrectly or at the wrong place.

Add a comment. Active Oldest Votes. There are a few points to note: If you exclude any namespace declarations, things are considered to be in the default namespace. Improve this answer. Rob Levine Rob Levine You may want to qualify "Basically, every element or attribute in xml belongs to a namespace", since some elements and attributes are said to be in "no namespace". Though I understand you were giving the basics. Rob Levine "Attributes can be namespaced but are generally not. So how is for example " your.

Can you explain this as well please? When you define your query, you need to specify the namespace, probably via a prefix. In the C System. Xml world, for example, you'd register a prefix with the namespace manager using XmlNamespaceManager. AddNamespace, and then use this prefix in your query. The fact the prefix doesn't appear in the document doesn't matter - only what namespace it maps too.

This microsoft document link :" msdn. Show 9 more comments. It defines an XML Namespace. Mads Hansen Mads Hansen 56k 12 12 gold badges silver badges bronze badges. I always paste those URIs into a web browser just to see what the parser is looking at, but it always returns Is it supposed to be a real URI that needs a standard filename tacked on to the end, or is it just a technique for making a unique id?

Patrick yes, its just a URI that needs to be unique so as to indicate that it is a separate namespace from others and any potential duplicate tags will therefore be interpreted correctly. So the URI will often point to nothing. I used to wonder whether specifying a URI made the html page actually access that website to determine a schema. Note that Internet Explorer 5. For more information, see question 8.

To override the prefix used in an XML namespace declaration, you simply declare another XML namespace with the same prefix.

Using multiple default XML namespaces can lead to documents that are confusing to read and should be done carefully. For more information, see question 5.

You cannot "undeclare" an XML namespace prefix. It remains in scope until the end of the element on which it was declared unless it is overridden. Trying to undeclare a prefix by redeclaring it with an empty zero-length URI results in an error. Within the scope of this declaration, unprefixed element type and attribute names do not belong to any XML namespace. I don't know the answer to this question, but the likely reason is that they simplify the process of moving fragments of one document to another document.

While these were simple to read and process, they weren't easy to move to other documents. Attributes, on the other hand, were intimately attached to the elements being moved.

Make sure you have declared the prefix see question 4. All you need to do then is prefix the local name of an element type or attribute with the prefix and a colon. The result is a qualified name see question Note that the prefix is used on both the start and end tags. Make sure you have declared the default XML namespace see question 4. All you need to do then is use the local name of an element type.

Even though it is not prefixed, the result is still a qualified name see question For information about how to use the default XML namespace with attribute names, see question 5. The default XML namespace only applies to element type names, so you can refer to attribute names that are in an XML namespace only with a prefix.

In the following, the type attribute name does not refer to that namespace, although the Address element type name does. For information about how to use the default XML namespace with element type names, see question 5.

This is purely a matter of choice, although your choice may affect the readability of the document. When elements whose names all belong to a single XML namespace are grouped together, using a default XML namespace might make the document more readable.

When elements whose names are in multiple XML namespaces are interspersed, default XML namespaces definitely make a document more difficult to read and prefixes should be used instead. In some cases, default namespaces can be processed faster than namespace prefixes, but the difference is certain to be negligible in comparison to total processing time.

An XML namespace declaration remains in scope for the element on which it is declared and all of its descendants, unless it is overridden or undeclared on one of those descendants see questions 4. One consequence of XML namespace declarations applying to the elements they occur on is that they actually apply before they appear. Because of this, software that processes qualified names should be particularly careful to scan the attributes of an element for XML namespace declarations before deciding what XML namespace if any an element type or attribute name belongs to.

When an element or attribute is in the scope of an XML namespace declaration, the element or attribute's name is checked to see if it has a prefix that matches the prefix in the declaration. Whether the name is actually in the XML namespace depends on whether the prefix matches.

When an XML namespace declaration goes out of scope, it simply no longer applies. In addition to the declaration no longer applying, any declarations that it overrode come back into scope. If no XML namespace declaration is in scope, then any prefixed element type or attribute names result in errors. For example, in the following, the names foo:A and foo:B result in errors.

In the absence of an XML namespace declaration, unprefixed element type and attribute names do not belong to any XML namespace. For more information, see question 3. Yes, as long as they don't use the same prefixes and at most one of them is the default XML namespace. One consequence of this is that you can place all XML namespace declarations on the root element and they will be in scope for all elements. This is the simplest way to use XML namespaces.

XML namespace declarations that are made on the root element are in scope for all elements and attributes in the document. This means that an easy way to declare XML namespaces is to declare them only on the root element. XML namespaces can be declared only on elements and their scope consists only of those elements and their descendants. Thus, the scope can never include the DTD.

In particular, DTDs can contain qualified names see question 7. This situation has caused numerous complaints but, as XML namespaces are already a recommendation, is unlikely to change.

The long term solution to this problem is an XML schema language: all of the proposed XML schema languages provide a mechanism by which the local name in an element type or attribute declaration can be associated with an XML namespace. This makes it possible to redefine validity in terms of universal names. For more information, see question 4. As a result, qualified names in the DTD have no special meaning. The reason qualified names are allowed in the DTD is so that validation will continue to work.

The answer to this question is yes in the sense that a qualified name in a content model can have a different prefix than the qualified name of the element type being declared. For example, the following is legal:. The answer to this question is no in the sense that XML namespace declarations do not apply to DTDs so the prefixes used in an element type declaration are technically meaningless.

In particular, they do not specify that the name of a certain element type belongs to a certain namespace. Nevertheless, the ability to mix prefixes in this manner is crucial when: a you have a document whose names come from multiple XML namespaces see question 8. Thus, validity is the same for a document that uses XML namespaces and one that doesn't. In particular, with respect to validity:. Because of this, XML documents that you might expect to be valid are not.

Furthermore, documents that you might expect to be invalid are valid. Finally, validity has nothing to do with correct usage of XML namespaces. For example, the following document is valid but does not conform to the XML namespaces recommendation because the foo prefix is never declared:. Therefore, when constructing an XML document that uses XML namespaces, you need to do both of the following if you want the document to be valid:. There is no requirement that the same prefix always be used for the same XML namespace.

For example, the following is also valid:. However, documents that use multiple prefixes for the same XML namespace or the same prefix for multiple XML namespaces are confusing to read and thus prone to error.

They also allow abuses such as defining an element type or attribute with a given universal name more than once, as was seen earlier. Therefore, a better set of guidelines for writing documents that are both valid and conform to the XML namespaces recommendation is:.

The latter three guidelines guarantee that prefixes are unique. This means that prefixes fulfill the role normally played by namespace URIs -- uniquely identifying an XML namespace -- and that qualified names are equivalent to universal names, so a given universal name is always represented by the same qualified name.

Although this is contrary to the spirit of prefixes, which were designed for their flexibility, there is no other solution at this point.

When people ask this question, they usually assume that validity is different for documents that use XML namespaces and documents that don't. In fact, it isn't -- it's the same for both. Thus, there is no difference between validating a document that uses XML namespaces and validating one that doesn't.

In either case, you simply use a validating parser or other software that performs validation. For information about how to construct an XML document that is valid and conforms to the XML namespace recommendation, see question 7.

If you want your XML documents to be both valid and conform to the XML namespaces recommendation, you need to declare any xmlns attributes and use the same qualified names in the DTD as in the body of the document. For more information, see question question 7. To do this, declare the attribute xmlns no prefix for each possible root element type. If you can guarantee that the DTD is always read see question 4. If your DTD contains element type and attribute names from multiple XML namespaces, you need to choose a single prefix for each XML namespace and use these consistently in qualified names in both the DTD and the body of each document.

As in the single XML namespace case, the easiest way to do this is add xmlns attributes to each possible root element type and use default values if possible. The same as you create documents that don't use XML namespaces. If you're currently using Notepad on Windows or emacs on Linux, you can continue using Notepad or emacs.