Why aren't my XSLT variables substituting their values?

Question

I am trying to use XSLT variables and not having much success, hopefully I'm just doing something dumb.

I have the following code snippet:

<xsl:stylesheet
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:xalan="http://xml.apache.org/xslt"
  version="1.0">

    <xsl:template match="/">
      <xsl:variable name="config" select="query/@config"></xsl:variable>

so I expect there to be a variable 'config' set to the value of the 'config' attribute of my top-level element 'query'.

I then try to use the variable later in my stylesheet, for example:

<a href="localhost/test?go">
    {$config}
</a>

but the output I see in my output HTML document is:

<a href="localhost/test?go">
    {$config}
</a>

so the value has not been substituted as I would have expected.

I think this is pretty much the simplest case there could be, so I'm doing domething stupid! Please help, thanks!

---

UPDATE thanks to all who responded, I misunderstood the different contexts of whether I was working in an attribute or outside. Sorted my problem out nicely!

If I could I would accept two answers, the one I have, and @Aaron Digulla's, which explained the attributes thing.

Answer 1

Use <xsl:value-of select="$config"/> instead of {$config}.

Answer 2

Because you need to use <xsl:value-of select="config"/> ?

Answer 3

In your stylesheet you must use:

<xsl:value-of select="$config"/>

instead of:

{$config}

Answer 4

{$config} only works in attributes of XSLT elements. (Note: dollar inside the brace because the complete XPath expression must be surrounded by braces)