More on the Trends API: It seems that only III (supermodal) is treated as identical to V/vi so that Theorytabs in Minor mode can use V, but not other secondary dominants; and I believe that for the same reason only #v° is realized as vii°/vi but not other secondary leading-tones none of the borrowed diminished chords are realized as equivalent secondary leading-tones even when they exist. Supermodal chords not recognized by the Trends API will cause no difficulty to be assigned to the Theorytabs, so I hope this observation could help rectify certain enharmonic chords before implementing the popular music style Roman numerals in the API.