1-based scale degree to tonicize: 5 is the dominant, so
secondaryDominant(5, majorKey(0)) is the V of V.
The prevailing key, as a key name, a key/scale, or a Key.
A dominant-seventh chord a fifth above the target's root.
secondaryDominantOf to tonicize a chord that has no degree in the key, or when no key is at hand.
The secondary dominant (V7) that tonicizes a scale degree.