Select all entries with asset field attribute criteria OK so I got entries articles with an asset field documents.
This asset field has an attribute called docType which is a dropdown with 5 values (A, B, C, D, E).  

I d like to select all articles entries that have documents with docType=A criteria.

How can I dot that?
Should I make a relatedTo selection?
I tried multiple things but nothing works.
You can do it like explained in this answer, only that you also add your dropdown field parameter to your craft.assets criteria model:

{% set assets = craft.assets.docType('A').limit(null) %}


and then:

{% set entries = craft.entries.section('articles').relatedTo({
    targetElement: assets,
    field: 'documents'
}) %}