+@item
+@code{horizontal-shift}
+
+@cindex horizontal-shift property
+@cindex note column
+@cindex note collisions
+@cindex collisions, notes
+@cindex shift commands
+@funindex \shiftOff
+@funindex shiftOff
+@funindex \shiftOn
+@funindex shiftOn
+@funindex \shiftOnn
+@funindex shiftOnn
+@funindex \shiftOnnn
+@funindex shiftOnnn
+
+Within a voice, all the notes occuring at the same musical moment are
+grouped into a note column, and a @code{NoteColumn} object is created
+to control the horizontal positioning of that group of notes (see
+@qq{Note columns} in @ref{Explicitly instantiating voices}). If
+@emph{and only if} two or more note columns within a single Staff
+context, both with stems in the same direction, occur at the same
+musical moment, the values of their @code{horizontal-shift} properties
+are used to rank them and the columns in the higher ranks are
+progessively offset to avoid collisions of the noteheads. This
+property is set by the @code{\voiceXXX} commands and may be overridden
+directly with an @code{\override} command or, more usually, by the
+@code{\shiftOn} commands. Note that this property is used to
+@emph{rank} the note columns for off-setting - it does not specify the
+magnitude of the offset, which is progressively increased in steps
+based on the note head's width for each rank. The steps are usually
+of half a note head's width, but may be a full note head's width when
+a closely spaced group of notes is involved.
+