A position in some source file. In the most common case, the source file is an Eiffel source
file, but, POSITION objects are also used in -cecil file or in the ACE file as well.
Because POSITION objects are very numerous (there are a _lot_ of POSITION objects used and
POSITON objects are small objects). For this reason, POSITION is an expanded class.
Note: do not add new attributes in this class which must fit on 32bits. Also keep in mind that
it is an expanded class !