EXTERNAL specifies that the associated name is to have a scope of
declaration which consists not only of the declaring block (and its contain
blocks) but which also includes any other blocks containing an
explicit declaration of the same name which specifies the EXTERNAL
scope attribute. In other words, all declarations of a given name
containing the EXTERNAL scope attribute are to be treated as if referring
to the same item. Names with external scope are limited in length to 7
characters; longer names are abbreviated to the first 4 and last 3 characters
of the name.
EXTERNAL is the default for programmer-defined conditions and for file
and entry constants. All other items (including variables with any
storage class and entry names of internal procedures) are assigned
INTERNAL as a default.