How to make rallentando affect MIDI output?

[Martin Guy]

Hi! I've been searching the manula for over an hour trying to find out
how to make a rall from an initial tempo to a slower one sffect the
MIDI output.

I've found soeme mention of this in the articulate.ly script, but also
remember finding a notation in the manual to do this, which produced a
score notation where the beams of a semiquaver sequence were in their
usual places at one end but ended in the same position at the other,
giving a sort of triangular "fan-shaped" set of beams.

I've been searching the notation manual and the web for over an hour
without succeeding in finding this again. Does anyone happen to
remember what it's called or where it's documented?

Thanks & sorry for my laziness!

    M