i want to know, is there any real meaning of xmlns urls in xml document ?

i had refer to [link](http://www.w3schools.com/xsl/tryxslt.asp?xmlfile=cdcatalog&xsltfile=cdcatalog) . now when i change the `xmlns:xsl="http://www.w3.org/1999/XSL/Transform"`
to something else, it stopped working. w3c says namespace names(OR URL) is just for to distinguish xml tags. than why it is not working after changing url.

so i thought, may be it has something to do with that URL, so tried localy (without internet).. see following example..

XML Document. (first.xml)

```
<?xml version="1.0" encoding="ISO-8859-1"?>
<?xml-stylesheet type="text/xsl" href="first.xsl"?>
<!-- Edited by XMLSpy® -->
<catalog>
    <cd>
        <title>Unchain my heart</title>
        <artist>Joe Cocker</artist>
        <country>USA</country>
        <company>EMI</company>
        <price>8.20</price>
        <year>1987</year>
    </cd>
     <cd>
        <title>Pavarotti Gala Concert</title>
        <artist>Luciano Pavarotti</artist>
        <country>UK</country>
        <company>DECCA</company>
        <price>9.90</price>
        <year>1991</year>
    </cd>
    <cd>
        <title>The dock of the bay</title>
        <artist>Otis Redding</artist>
        <country>USA</country>
        <company>Atlantic</company>
        <price>7.90</price>
        <year>1987</year>
    </cd>
</catalog>

```

XSLT Document (first.xsl)

```
<?xml version="1.0" encoding="ISO-8859-1"?>
<!-- Edited by XMLSpy® -->
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:template match="/">
  <html>
  <body>
  <h2>My CD Collection</h2>
    <table border="1">
      <tr bgcolor="#9acd32">
        <th>Title</th>
        <th>Artist</th>
      </tr>
      <xsl:for-each select="catalog/cd">
      <tr>
        <td><xsl:value-of select="title"/></td>
        <td><xsl:value-of select="artist"/></td>
      </tr>
      </xsl:for-each>
    </table>
  </body>
  </html>
</xsl:template>
</xsl:stylesheet>

```

so, its working fine localy. but if i change `xmlns:xsl="http://www.w3.org/1999/XSL/Transform"` to something else like `xmlns:xsl="http://www.abc.com"` it gives me error in the browser.

```
Error loading stylesheet: Parsing an XSLT stylesheet failed.

```

so, the only question is, is there any real meaning of this URLS in xmlns. if yes it has than why it did worked without internet and not by changing the url in xsl.