The standard, accepted order of instrumentation for large ensembles: fl.ob.cl.bsn - hn.tpt.trbn.tba - perc - other - vlnI.vlnII.vla.vlc.db - tape, or electronics. Saxophones appear between clarinet and bassoon.
All other scorings (less than 8 instruments) are listed in full.
When an instrument is listed in parentheses, then this instrument is doubled. "guitar (=electric guitar)" means that the guitarist plays an acoustic, as well as an electric guitar. In an orchestral setting, "1(I=picc).2(II=corA).2(II=bcl).1" would resolve to: 1 flute (also playing piccolo), 2 oboes (second oboe also playing cor anglais), 2 clarinets (second clarinet also playing bass clarinet), 1 bassoon. If there is an extra instrument, which is not doubled, then this is expressly written out, e.g. "1(I=picc).2.corA.2.bcl.1.dbn", which unravels to: 1 flute (also playing piccolo), 2 oboes, 2 clarinets, 1 bass clarinet, 1 bassoon, 1 double bassoon.
Solo instruments in a concerto or chamber setting are written out in front of the ensemble instruments: guitar - 220.127.116.11 - 18.104.22.168 - perc - strgs.
Book: Arthur Laurents; Lyrics: Stephen Sondheim
New York, Winter Garden Theatre, 26 September 1957: Jerome Robbins, choreographer and director / Max Goberman, conductor
Orchestrations: Sid Ramin, Irwin Kostal and Leonard Bernstein