How do I comment out an XML section that has comments inside?

The following won't work. It only comments out stuff0:

<!--
stuff0
<!-- stuff1 -->
stuff2
<!-- stuff3 -->
stuff4
<!-- stuff5 -->
stuff6
-->

Solution

-- is not allowed in XML comments. You can add a space between the two -. If you want to do that programmatically, an XSLT may do the job for you. For example, the following XSLT:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"  version="2.0">
    <xsl:template match="/">
        <a>
            <xsl:comment select="'a -- b -- c'"/>
        </a>
    </xsl:template>
</xsl:stylesheet>

Gives the following output:

<a><!--a - - b - - c--></a>

But the XSLT processor may also output an error. Given the specification, it's up to the implementation to add a space or raise an error.