The following bug has been logged on the website:
Bug reference: 14201
Logged by: Dilian Palauzov
Email address: dpa-postgres(at)aegee(dot)org
PostgreSQL version: 9.5.3
Operating system: Documentation
Description:
doc/sgml/ref/psql-ref.sgml > Advanced Features > Prompting > %R forgets to
state, that in prompt 2 the substitution can be open parenthesis, as seen
in the beginning of the Examples section.
https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=doc/src/sgml/ref/psql-ref.sgml#l3632