How to tell if a string is xml?

Question

We have a string field which can contain XML or plain text. The XML contains no header, and no root element, i.e. is not well formed.

We need t

Answer 1

If the XML contains no root element (i.e. it's an XML fragment, not a full document), then the following would be perfectly valid sample, as well - but wouldn't match your detector:

foobaz

In fact, any text string would be valid XML fragment (consider if the original XML document was just the root element wrapping some text, and you take the root element tags away)!