Parallel (concurrent) inserts?

Hello,

I'm wondering if there is ia document describing which guarantees (if
any) PostgreSQL makes about concurrency for various operations? Speaking
in general (i.e. IO can handle it, number of CPU cores and client
threads is optimal), are fully concurrent operations (independant and
non-blocking) possible for:

1) An unindexed table?

2) A table with 1+ ordinary (default btree) indexes? (are there
constraints on the structure and number of indexes?)

3) A table with 1+ unique indexes?

4) A table with other objects on it (foreign keys, check constraints, etc.)?