What is a namespace in XML?

Namespace in XML (XML Namespace) is a mechanism that prevents name collisions of elements and attributes in XML documents by grouping different XML vocabularies.

Main points:

• Defined by a URI (Uniform Resource Identifier). Although it is often a URL, URI does not necessarily have to be accessible over the network.
• Bound to elements and attributes using a prefix (e.g., xsl:template) or by default.
• The prefix is declared at the start of an element using the attribute xmlns:prefix="URI_of_namespace".
• To set a default namespace, use the attribute xmlns="URI_of_namespace".

Example:

<root xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
      xmlns="http://example.com/default-namespace">
    <xsl:template match="/">...</xsl:template>
    <element_from_default_namespace>...</element_from_default_namespace>
</root>

Here, xsl:template belongs to the XSLT namespace, and element_from_default_namespace belongs to "http://example.com/default-namespace".