I need to embed arbitrary (syntactically valid) XML documents within a wrapper XML document. The embedded documents are to be regarded as mere text, they do not need to be parseable when parsing the wrapper document.
I know about the "CDATA trick", but I can't use that if the inner XML document itself contains a CDATA segment, and I need to be able to embed any valid XML document. Any advice on accomplishing this--or working around the CDATA limitation--would be appreciated.
You need to properly escape the text. You don't say what language you're using, but generally: you build a DOM, create a Text node that contains your "inner" XML, and then serialize that DOM. The serializer will handle escaping for you.
The key point here is use a serializer to produce your output. Don't simply write strings, because you're all but guaranteed to produce something that's not well-formed XML.
When you escape the ending angular bracket of the inner CDATA, most XML parsers will not complain about the well-formedness of your XML. Using this "workaround", you should be able to nest multiple CDATA sections.
Something like:
<?xml version="1.0"?>
<SomeData>
<![CDATA[
<SomeMoreData>
<![CDATA[
yeah, this trick rocks! ...
]]>
</SomeMoreData>
]]>
</SomeData>
Note that the inner CDATA has its ending ">" escaped as >.
Consider using XInclude instead of trying to embed an XML document inside another. The XInclude parse="text" attribute will force the XML to be treated as text, not markup.
One easy solution is that you can have adjacent CDATA sections. <![CDATA[A]]><![CDATA[B]]> is the same as <![CDATA[AB]]>. Hence, you can have <![CDATA[]]]]><![CDATA[>]]>, a ]]> close tag split over two CDATA sections.
You can do this by simply adding the document (without its <?xml declaration) as a child tom some parent. SOAP is doing this - it has a <Body> element that can contain whatever xml message one wants to send.
SOAP defines the XSD this way:
<xs:element name="Body" type="tns:Body" />
<xs:complexType name="Body">
<xs:sequence>
<xs:any namespace="##any" minOccurs="0"
maxOccurs="unbounded" processContents="lax" />
</xs:sequence>
<xs:anyAttribute namespace="##any" processContents="lax">
</xs:anyAttribute>
</xs:complexType>