The following documentation comment has been logged on the website:
Page: https://www.postgresql.org/docs/16/plpgsql-statements.html
Description:
The last example in the chapter uses a named parameter "username". As a
result, the detail message should use "username" instead of "$1" to match
the runtime behaviour.
I suggest to change this line
DETAIL: parameters: $1 = 'nosuchuser'
to
DETAIL: parameters: username = 'nosuchuser'