Does it? My recollection is that the entry points were undocumented, and changed in every revision, of which there were at least 6! - BASIC 1, BASIC 2, HIBASIC,

Does it? My recollection is that the entry points were undocumented, and changed in every revision, of which there were at least 6! - BASIC 1, BASIC 2, HIBASIC, BASIC 4, BASIC 4.32, HIBASIC 4.32... The inbuilt assembler was super useful, and an excellent feature, but not obviously designed for calling BASIC itself. The expected use case seemed to be that you'd use BASIC by writing BASIC code, and any machine code routines (probably created using the inbuilt assembler) would be self-contained. (Modern readers unfamiliar with this system should compare the BBC BASIC assembler much more to LuaJIT's dynasm, which it rather resembles, than to the average C compiler's inline assembler, which it was not really much like.)