xml nombres de espacio

[mpozo]

The value of this attribute must be a fully-qualified URI (local paths and empty strings are not permitted). The URI will not be resolved when the document is parsed, and in fact it doesn’t need to point to an actual resource at all; the use of URIs is simply to ensure that namespaces are predictably unique to their creator.

Información obtenida de http://reference.sitepoint.com/html/html/xmlns

The namespace declaration is provided by the*xmlns*attribute. This attribute says that the*<svg>*tag and its child tags belong to whichever XML dialect has the namespace name*'http://www.w3.org/2000/svg'*which is, of course, SVG. Note the namespace declaration only needs to be provided once on a root tag. The declaration defines the*defaultnamespace, so the user agent knows that all the*<svg>*tag's descendant tags also belong to the same namespace. User agents check to see if they recognize the namespace name to determine if they know how to handle the markup.
Note that namespace names are just strings, so the fact that the SVG namespace name also looks like a URI isn't important. URIs are commonly used because they are unique, the intention is not to "link" somewhere. (In fact URIs are used so frequently that the term "namespace URI" is commonly used instead of "namespace name".)

Información obtenida de https://developer.mozilla.org/en-US/...s_Crash_Course