A processing instruction begins with <? and ends with ?>. The ModelTools schema uses one processing instruction: include. This processing instruction is used to include a file into the XML document at the position of the processing instruction.
<?include MyNearbyFile ?>
The include file names are relative to the location of the include processing instruction. This means that a simple file name can typically be used. The parser's file manager keeps up with the other requisite details.
There is also a processing instruction like element called the XML declaration that details the version of XML that is being used. For example
<?xml version=1.0' ?>
The XML declaration should be the first element in the document. But it is optional and in this schema it is honored wherever it is and then it is ignored.