Thanks!
Its not quite that what I need but thank you anyway. The problem is I want to pick the cards by tag and merge them not isolate them by tag.
E.g.: 100 cards (notes) have tag "A" and another 200 tag "B" but none of those cards have been tagged "A" and "B". It ends up that not only 1 card is being skipped to the filtered deck. The keyword "or" I have also tried and it seems to be that what I need but it didnt worked. When I search for "TAG:A or TAG:B" it builts up a deck with only cards which are tagged "A".
Edit:It worked!! "OR" was the clue! Thank you Tim! Is there a list of "keywords" somewhere?
Cheers!