Default Setting for PDO::ATTR_EMULATE_PREPARES

I have read that, by default, PDO::ATTR_EMULATE_PREPARES is false. 
However, I have also read that this is not true for all database 
connections — PostgreSQL defaults to true.

The point is, this is all coming from third parties. As knowledgeable as 
they are, I would prefer to check with the source.

Where is the default setting for PDO::ATTR_EMULATE_PREPARES documented?

Thanks