This article is a copy of http://kybest.hu/en/blog/entity-reference-customizability-at-its-best from google cache. I found it usefull
#Entity reference - customizability at its best
Submitted by CZÖVEK András on 2013-11-26, Tuesday, 17:29 The Entity reference module is one of the most used Drupal modules. At the moment of writing it is 51st on the usage list of Drupal projects. Those who have already made a Drupal site probably have knows it. At the same time, not many know what a powerful tool it can be even in special cases.
The quality of a Drupal module is quite well characterized by its customizability. If a module produces markup for instance we expect to be able to alter that markup through the theme layer of Drupal. The Entity reference is an excellently written module in this aspect (too). But what should be customized in the Entity reference module?
In one of the sites recently produced by us one part of the content comes from an external source. These contents are digitalized books stored on t