How to get current instance name from T-SQL

Question

How can I get the SQL Server server and instance name of the current connection, using a T-SQL script?

Answer 1

Just found the answer, in this SO question (literally, inside the question, not any answer):

SELECT @@servername

returns servername\instance as far as this is not the default instance

SELECT @@servicename

returns instance name, even if this is the default (MSSQLSERVER)