I do expect a problem for you, if you want to create and handle all the possible permutations of Publishers and Composers.
And for what should it be worth?
Or do I misunderstand the problem?
Maybe you only want to get each single item from a list of items?
But there is no loop or foreach instruction, which works directly on the content of a tag-field, ...
therefore you have to do it the hard way, extract each single item from the itemlist, which is stored within one tag-field, step by step.
For example ... you can count the commas within a string (3 commas = 4 items), ...
and then decide, using $if, which case of a set of prepared cases, is able to handle this number of items.
For example ... you can try this sort of regular expression ...
$regexp('Aaa, Bbb, Ccc, Ddd, ','^(?:.+?, ){0}(.+?), (?:.+, )*$','$1') ==> 'Aaa'
$regexp('Aaa, Bbb, Ccc, Ddd, ','^(?:.+?, ){1}(.+?), (?:.+, )*$','$1') ==> 'Bbb'
$regexp('Aaa, Bbb, Ccc, Ddd, ','^(?:.+?, ){2}(.+?), (?:.+, )*$','$1') ==> 'Ccc'
$regexp('Aaa, Bbb, Ccc, Ddd, ','^(?:.+?, ){3}(.+?), (?:.+, )*$','$1') ==> 'Ddd'
DD.20150305.1854.CET
Hmm, here is another idea, ...
how to split an itemlist into single addressable items, ...
by creating a multi-value tag-field from the tag-field, which contains the string with the itemlist.
-
Copy the existing content from COMPOSER to new tag-field COMPOSER_META, ...
e. g. the list of items is 'Aaa, Bbb, Ccc, Ddd'
-
Run Action "Split field by separator", ...
Field: COMPOSER_META
Split character: ,
-
Then there exists a multi-value tag-field COMPOSER_META.
COMPOSER_META = 'Aaa'
COMPOSER_META = 'Bbb'
COMPOSER_META = 'Ccc'
COMPOSER_META = 'Ddd'
Each value can be accessed directly by using the function $meta.
$meta(COMPOSER_META,0) ==> 'Aaa'
$meta(COMPOSER_META,1) ==> 'Bbb'
$meta(COMPOSER_META,2) ==> 'Ccc'
$meta(COMPOSER_META,3) ==> 'Ddd'
This might be useful when creating an export script, ...
which probably can have simpler coding needed than the $regex proposal.
After creating the report, the multi-value tag-field COMPOSER_META can be removed from the tag, using the ...
Action "Remove fields"
Field: COMPOSER_META
DD.20150305.2109.CET