It provides one-to-one correspondence functions of most DXC ++ API, including interfaces of DX 10, Xinput, XAudio and XACT. Currently mature and stable.
It is the environment in which software can run, which is called software runtime. This translation is a bit awkward, and there seems to be no better translation at present. For example, many Java programs need JRE(Java runtime environment), like eclipse, without JRE, they can't run.