How to create index on JSON field in Postgres?

In PostgreSQL 9.3 Beta 2 (?), how do I create an index on a JSON field? I tried it using the -> operator used for hstore but got the following error:

 CREATE TABLE publishers(id INT, info JSON);
 CREATE INDEX ON publishers((info->'name'));

ERROR: data type json has no default operator class for access method "btree" HINT: You must specify an operator class for the index or define a default operator class for the data type.

Solution 1:

Found:

CREATE TABLE publishers(id INT, info JSON); 
CREATE INDEX ON publishers((info->>'name'));

As stated in the comments, the subtle difference here is ->> instead of ->. The former one returns the value as text, the latter as a JSON object.