A 2-line staff is used, with the lower line representing E. Above and below the staff a ledger line is used to represent C. Between any two adjacent lines there are three elevations on which notes can be placed. These elevations are made easier to distinguish because the notehead is given a semicircular shape when it rests against a line. Rhythmic notation is mostly traditional.
In Chromatic Twinline the notehead color alternates in a 6-6 pattern, with the semicircles black and the ovals white. (In Diatonic Twinline the notehead color corresponds to the 7-5 pattern of the piano key color.)
Earliest documentation: 1986
Source: Directory of Music Notation Proposals, section/page: 10/11, 11/2, 13/25