-The notes in the third measure appear only once, although they were
-specified in both parts. Stem, slur, and tie directions are set
-automatically, depending whether there is a solo or unison. When
-needed in polyphony situations, the first part (with context called
-@code{one}) always gets up stems, while the second (called @code{two})
-always gets down stems. In solo situations, the first and second
-parts get marked with @qq{Solo} and @qq{Solo II}, respectively. The
-unison (@notation{a due}) parts are marked by default with the text
-@qq{a2}.
-
-Both arguments to @code{\partcombine} will be interpreted as
-@code{Voice} contexts. If using relative octaves,
-@code{\relative} should be specified for both music expressions,
+Both parts have identical notes in the third measure, so only one
+instance of the notes is printed. Stem, slur, and tie directions are
+set automatically, depending on whether the parts are playing solo or in
+unison. When needed in polyphony situations, the first part (with
+context called @code{one}) gets @qq{up} stems, while the second (called
+@code{two}) always gets @qq{down} stems. In solo situations, the first
+and second parts get marked with @qq{Solo} and @qq{Solo II},
+respectively. The unison (@notation{a due}) parts are marked with the
+text @qq{a2}.
+
+By default, the partcombiner merges two notes of the same pitch as an
+@notation{a due} note, combines notes with the same
+rhythm less than a ninth apart as chords and separates notes more than
+a ninth apart (or when the voices cross) into
+separate voices. This can be overridden with an optional argument of a pair
+of numbers after the @code{\partcombine} command: the first specifies
+the interval where notes start to be combined (the default is zero) and the
+second where the notes are split into separate voices. Setting the second
+argument to zero means that the partcombiner splits notes with an interval of
+a second or more, setting it to one splits notes of a third or more, and so on.
+
+@lilypond[quote,verbatim]
+instrumentOne = \relative {
+ a4 b c d |
+ e f g a |
+ b c d e |
+}
+
+instrumentTwo = \relative {
+ c'4 c c c |
+ c c c c |
+ c c c c |
+}
+
+<<
+ \new Staff \partcombine \instrumentOne \instrumentTwo
+ \new Staff \partcombine #'(2 . 3) \instrumentOne \instrumentTwo
+>>
+@end lilypond
+
+
+Both arguments to @code{\partcombine} will be interpreted as separate
+@code{Voice} contexts, so if the music is being specified in relative
+mode then @emph{both} parts must contain a @code{\relative} function,