Anyway, from my recollection, it was a case of me wanting to produce a C++ API/wrapper around the C API, and realising that the extant documentation wasn't quite sufficient for me to do so (to fully grok what went on underneath the C API enough to produce a C++ wrapper). Therefore, producing a more thorough technical reference manual seemed to me to kill 2 birds: I'd obtain a sufficient understanding, and so would the customers. Thus although Jez was right that the manual came first, the process of producing a more thorough TRM gave rise to Sam's observations.