RPSL question

Dear Colleague,

I'm writting a Perl RPSL parser module and have a understanding
problem with part 2 "RPSL Names, Reserved Words, and Representation" 
page 5 of RFC 2622 ;-(

  "A value of an attribute may also be a list of one of these types.  A
   list is represented by separating the list members by commas ",".
   For example, "AS1, AS2, AS3, AS4" is a list of AS numbers.  Note that
   being list valued and being multiple valued are orthogonal.  A
   multiple valued attribute has more than one value, each of which may
   or may not be a list.  On the other hand a single valued attribute
   may have a list value."

Ok, a multiple attribute value can be a single value or a 'comma list'
of values. But the last sentence confused me - "a single valued
attribute may have a list value" ?

Means that "aut-num: AS123, AS456, ..." is a correct attribute of
an aut-num object ?!?!


Cheers
Frank