What characters are never used in xpath?

Question

I'm trying to build a DSL which will contain a number of XPaths as parameters. I'm new to XPath, and I need a character which is never used in the XPath syntax so I can delimit n number of XPaths on a single line of a script. My question: what characters are NOT part of the XPath syntax?

Answer 1

The null character.

Seriously. Because an XPath is supposed to support any XML document, it must be capable of matching text nodes that contain any allowed Unicode character. However, XML disallows one character: the null character.

Ok, that is not entirely true, but it is simplest. As in XML 1.1, control characters were supported, except Unicode Null. However, as per the XML 1.0 production of Char, there are a few other characters you can choose from: surrogate pairs (as characters, not as correctly encoded octets representing a non-BMP character), and anything before 0x20, except linefeed, carriage return and tab.

Another good guess is any Private Use character, as it is unlikely it is used by your input documents, however, this is not guaranteed, and you asked for "never".