Subsection 4.28.4 Characters in URLs
A URL can have a query string, which has a list of parameters following a question-mark. The parameters are separated by ampersands (&), which will need to be escaped, so as to not confuse the XML processor. So use
& anywhere the ampersand character is necessary, such as a @source attribute, or a monospace version of a URL achieved with a <c> element. Also, the question-mark character should not be URL-encoded (%3F) (despite advice just given above), so if necessary edit it to be the actual character. General advice about exceptional characters in XML source can be found in Section 3.14.
