The following documentation comment has been logged on the website:
Page: https://www.postgresql.org/docs/10/static/plpgsql-trigger.html
Description:
The documentation (10 and 9.6) contains a typo when mentioning 'Special
local variables PG_something'. Instead it should be 'Special local variables
TG_something' as it is for trigger local variables.
Examples just below all start with TG_ so it should be obvious.