Compatible collections SOLR4 / SOLRCloud?

[Marcin]

Hi there,

I am trying to figure out what SOLR means by compatible collection in 
order to be able to run the following query:

Query all shards of multiple compatible collections, explicitly specified:

http://localhost:8983/solr/collection1/select?collection=collection1_NY,collection1_NJ,collection1_CT

Does this mean that the schema.xml must be exactly same between those 
collections or just partially same (share same fields used to satisfy 
the query)?

cheers,
/Marcin