A     B      C     D        <-- labels
$x = ( $i, $j ) = ( $p, $q ); 
S  ?   L L L    S   L L L      <-- context
|  |   | | |    |   | |  \__ Propogated by right-most list op'tor (D).
|  |   | | |    |   |  \____ Imposed by the list assignment (C).
|  |   | | |    |    \______ Propogated by right-most list op'tor (D).
|  |   | | |     \__________ Imposed by the scalar assignment (A).
|  |   | |  \_______________ Propogated by left-most list op'tor (B).
|  |   | \__________________ Imposed by the list assignment (C).
|  |    \___________________ Propogated by left-most list op'tor (B).
|   \_______________________ Determined by outside code.
 \__________________________ Imposed by scalar assignment (A).