Type Alias KeyRegion

First beat of the region.

End of the region, exclusive.

The key in force across the region, owned by it: every entry point hands back a key of the region's own, so writing to one changes neither the other regions of the same run nor what a later call reports.

Whole, whichever way the region was built. A caller who named the key hands its spelling and scale form down, and a key the analysis found is spelled and formed the way resolveKey reads a bare scale — the reading every other layer would have made of it. There is no third state to guess at: a key/scale alone says nothing about how it is written, so a region carrying one would report whichever spelling those pitch classes read best from, and an Ab minor handed in would come back out a G# minor.

How well the region's music fits the key, in [0, 1]: the correlation between the span's pitch-class distribution and the key's profile, with negative correlations reported as 0.

One statistic whichever entry point built the region, so a threshold or a comparison means the same thing across them. Where the region came from chords rather than notes, the distribution is each chord's tones weighted by how long the chord holds.

How this key relates to the previous region's — 'dominant' for a move to the dominant, 'relative' for a move to the relative minor, and so on. Absent on the first region, and absent when the two keys stand in none of the named relations.

Never 'same': a region is the maximal span of one key, so consecutive regions never share one and a region carrying this field is a place the piece moved.

The chord the modulation turned on, when one was identified. Only the chord-aware entry points fill this in: a pivot is a chord that reads in both keys, so it cannot be named without knowing which chord sounded.