Feeds XPath Parser implements XPath 1.0 in Feeds, allowing the selection of nodes from an XML document. The XPath language is based on a tree representation of the XML document, and provides the ability to navigate around the tree, selecting nodes by a variety of criteria. In addition, XPath may be used to compute values (strings, numbers, or boolean values) from the content of an XML document.
It should also be mentioned that if you want to import different "projects" to different nodes from the example above - you should set "Context" from "XPath Parser Settings" to "/wikimedia/projects/project". And then add something like "editions/*" for the second value of the "edition" field.