Super class for all petal objects that have access qualifiers, i.e.,
"Public", "Protected", "Private", or "Implementation" (whatever that means, probably
it reads "language dependent")
Denote that a petal object contains a reference to another object via
the property "supplier", i.e., a fully qualified name like
"Logical View::University::Professor".
This method is strict in that it does not use equals() to search
the list of properties but ==, since values, in particular
literals may occur more than once.
Print petal file exactly like Rose would with some limitations concerning
indendattion, i.e., if you don't mind white space, input and output files are
identical.