That document is defining the protocol for error fields, and it's the client's responsibility to parse and present them. (i.e. psql
, JDBC
or something else).
W
is meant to provide the context
for the error in the form of a stack trace, so a sense of where the error occurred can be reflected to the user of the client.
What is the context for this question? i.e. why do you want to know the protocol specifics?