Directives: define

This directive defines a chord in terms of fret/string positions and, optional, finger settings.

{define: name base-fret offset frets pos pos … pos}
{define: name base-fret offset frets pos pos … pos fingers pos pos … pos}

name is the name to be used for this chord. If it is an already known chord the new definition will overwrite the previous one.
base-fret offset defines the offset (the lowest fret) for the chord. The offset must be 1 or higher.
frets pos pos … pos defines the string positions, all relative to the offset. 0 (zero) denotes an open string. Use N or x to denote a non-sounding string.

Strings are enumerated from left (lowest) to right (highest), as they appear in the chord diagrams.

fingers pos pos … pos defines finger settings. This part may be omitted.

For the frets and the fingers positions, there must be exactly as many positions as there are strings, which is 6 by default. For the fingers positions, values corresponding to open or damped strings are ignored.

Example:

{define: Bes base-fret 1 frets 1 1 3 3 3 1 fingers 1 1 2 3 4 1}
{define: As  base-fret 4 frets 1 3 3 2 1 1 fingers 1 3 4 2 1 1}

The resultant chord diagrams are:

The asterisk after the chord names indiciates that the chords have been defined in the song, possibly overriding built-in definitions.