Using an XSL Element (?) as a URL in an <a> tag in Symphony CMS

I have just started trying to get my head around Symphony and XML/XSL based templating etc (I don't even know the correct terminology so forgive me).

I have a Videos section in Symphony, and one of the Input fields is for a YouTube URL. I obviously can't just write <a href="<xsl:value-of select="youtube-url"/>">Video</a> but I'm really not sure how it SHOULD be done.

I did some Googling and found that xml/xsl or whatever supports variables so I thought that was a good shout, but as you can see in my code example below, whatever I have done, it has failed. Maybe I'm just using variables wrong? I don't know.

I just need my Youtube-URL to be in the space that I currently have {$youtube}

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:include href="../utilities/master.xsl"/>
<xsl:variable name="youtube"> 
    <xsl:value-of select="youtube-url"/>
</xsl:variable>
<xsl:template match="data">
    <div class="video-container">
        <xsl:apply-templates select="videos/entry"/>
    </div>
</xsl:template>
<xsl:template match="videos/entry">
    <div class="video">
        <div class="video-title"><xsl:value-of select="title"/></div>
        <div class="video-player">
            {$youtube}
        </div>
        <div class="video-desc"><xsl:value-of select="description"/></div>
    </div>
</xsl:template>
</xsl:stylesheet>

Solution

You can't write

<a href="<xsl:value-of select="youtube-url"/>">Video</a>

but you can write

<a href="{youtube-url}">Video</a>

<a href="{$youtube}">Video</a>

That's an attribute value template.

It only works in within attributes, though. You cannot use it in other text. (something like <div class="video-player">{$youtube}</div> will not work - use <xsl:value-of> instead.)