What's a namespace?

<script type="text/javascript"> google_ad_client = "pub-8800625213955058"; /* 336x280, 创建于 07-11-21 */ google_ad_slot = "0989131976"; google_ad_width = 336; google_ad_height = 280; // </script> <script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"> </script> Randall Fowle writes: A namespace is a collection of element and attribute names identified by a Uniform Resource Identifier reference. The reference appears in the root element as a value of the xmlns attribute. For example, the namespace reference for an XML document with a root element x might appear like this: . More than one namespace may appear in a single XML document, to allow a name to be used more than once. Each reference can declare a prefix to be used by each name, so the previous example might appear as , which would nominate the namespace for the `spc' prefix: Mr. Big . The reference does not need to be a physical file; it is simply a way to distinguish between namespaces. The reference should tell a person looking at the XML document where to find definitions of the element and attribute names using that particular namespace.