What is the minimum supported Servlet version?

[jtotht]

According to README.md, OpenCms 17 (and also the upcoming OpenCms 18) require a Servlet 4.0-compatible servlet container, for example Tomcat 9. However, according to INSTALL.md (as well as the actual web.xml file), the minimum requirement is Servlet 3.1 (e.g. Tomcat 8.0). So is Servlet 3.1 / Tomcat 8.x supported in either OpenCms 17 or OpenCms 18? If not, could web.xml be updated to reflect this (preferably in 18; if it’s too late, then in 19), so that local customization can take advantage of Servlet 4.0 features?