The song strip figure
A bar a column, the chord's numeral above and its tones lit across the pitch rows in the key's colors, the tune traced through them with a degree on every note wide enough for one — a melody, what was under it, and what each note is against that.
The song strip is Bard's picture of a phrase: where the melody went, what was sounding under it, and what each note is against that. Tap a tile to hear it — and the text follows.
On the chord
Time runs left to right, a bar a column, with the chord's numeral above each bar. Pitch runs up the strip, a row a semitone, and each bar's chord lights the rows of its tones in the key's colors. The tune is the line — flat where a note holds, sloping where it moves — with a degree on every note wide enough to carry one. In this tile the line rests on the lit rows: the melody sits on the chord.
The key's other notes
Same chords, same rhythm, but the line now rests between the lit rows, on notes that are in the key and not in the chord. The three tiles differ in one thing only, so the difference is the lesson.
Outside the key
The notes now land off the key altogether — visibly off the rows, and you can hear why.
Hear it
A tapped tile plays round — chords on a guitar, the tune on a piano — and at every lap it is drawn again: the same rhythm and chords, the pitches rolled anew. The other tiles stay as they were, so the picture that changed is the one you are hearing. Tap the playing tile to stop; ↻ draws all the tiles afresh. Nothing here is written by hand: every tile is a draw from Bard's own melody engine, and every visit gets new ones.
Where you'll meet it
In Songwriting basics, where each of the five habits is two or three tiles that differ in one thing; at the opening of Why the major modes, one phrase from all twelve notes and from seven; and near the end of Notes, intervals and scales, one phrase in two keys.