This tests Multisource operations:

Sources                                : source1 source2

Eles                                   : eight five four one seven six three two

Eles_in_source (source1)               : eight five four one seven six three
Eles_in_source (source2)               : eight five four seven six three two

Ele_in_sources (one)                   : source1
Ele_in_sources (two)                   : source2
Ele_in_sources (three)                 : source1 source2
Ele_in_sources (zero)                  :

Ele_in_source (source1,one)            : 1
Ele_in_source (source1,two)            : 0

Ele (one)                              : 1
Ele (zero)                             : 0

Access (three,/a)                      : 
Access (three,/b)                      : 3b1
Access (three,/c)                      : 3c
Access (four,/l)                       : 2

Access (one,/l)                        : l1 l2
Access (one,/)                         : b c l

Which (/b bb)                          : one
Which (/c cc)                          : four one

Which_sources (zero /a all)            :
Which_sources (one /xxx all)           :
Which_sources (eight /c all)           : source1 source2
Which_sources (eight /c all-val)       : source1
Which_sources (eight /c readonly)      : source1 source2
Which_sources (eight /c readonly-val)  : source1