Hello,
In the Netherlands we have a profile on WFS 1.1.0. It is still in use. For this profile we have test tooling. The tooling requests a server, using the srsName with the following notation: "EPSG:28992". This is based on page 36 of the WFS 1.1.0 spec.
-- start quote page 36 --
Any valid URI value can be assigned to the srsName attribute. However, in order to enhance interoperability, a web feature service must be able to process srsName attribute values with the following format models:
EPSG:<EPSG code>
