Consider changing order of top-level domain elements

Martin Zien stated in the forum that it is desirable that the <metadata> element by default appears before the other top-level domains (<common>, <infrastructure>, <interlocking>, <rollingstock>, <timetable> and <visualizations>). According to the current specification, the elements can be listed in any order. The issue is that export interfaces following the order from the XSD (e.g. because the code was generated from the XSDs or UML) will list <metadata> between <interlocking> and <rollingstock>, rather than as the first element.

Martin Zien's suggestion is to reorder the elements in the XSD. This will not change the syntactic specification, and therefore not break any compatibility (it will still be legal to list the elements in any order). The goal is that export interfaces following the order from the XSD will list <metadata> first.

The implementation is simple if we agree that it is best practice to list <metadata> before the other elements.

Forum thread: https://www.railml.org/forum/index.php?t=msg&th=890&start=0&