I updated the Alternative Csound Reference Manual to edition 4.21-1. This manual covers the latest version of the Csound program, 4.21. If you don't know, Csound is a sound synthesis program: http://www.csounds.com/.
I added documentation for the following opcodes: a, butbp, butbr, buthp, butlp, cngoto, convle, else, elseif, endif, ftload, ftloadk, ftsave, ftsavek, ink, invalue, ktableseg, oscilx, outk, outvalue, reverb2, subinstr, and sense.
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You can always look at the on-line edition here: