instr i, j, ... . . < body . of . instrument > . endin
instr - begin an instrument block defining instruments i, j, ...
i, j, ... must be numbers, not expressions. Any positive integer is legal, and in any order, but excessively high numbers are best avoided.
endin - end the current instrument block.
There may be any number of instrument blocks in an orchestra.
Instruments can be defined in any order (but they will always be both initialized and performed in ascending instrument number order).
Instrument blocks cannot be nested (i.e. one block cannot contain another).