-produces naturally spaced lines (i.e., @code{raggedright = ##t}); this
-works well for small music fragments.
-
-@item linewidth=@var{size}\@var{unit}
-sets linewidth to @var{size}, where @var{unit} = cm, mm, in, or pt.
-This option affects LilyPond output, not the text layout.
+Produce ragged-right lines with natural spacing (i.e., @code{raggedright
+= ##t} is added to the LilyPond snippet). This is the default for the
+@code{\lilypond@{@}} command if no @code{linewidth} option is present.
+It is also the default for the @code{lilypond} environment if the
+@code{fragment} option is set, and no line width is explicitly
+specified.
+
+@item packed
+Produce lines with packed spacing (i.e., @code{packed = ##t} is added
+to the LilyPond snippet).
+
+@item linewidth
+@itemx linewidth=@var{size}\@var{unit}
+Set line width to @var{size}, using @var{unit} as units. @var{unit} is
+one of the following strings: @code{cm}, @code{mm}, @code{in}, or
+@code{pt}. This option affects LilyPond output (this is, the staff
+length of the music snippet), not the text layout.
+
+If used without an argument, set line width to a default value (as
+computed with a heuristic algorithm).
+
+If no @code{linewidth} option is given, @command{lilypond-book} tries to
+guess a default for @code{lilypond} environments which don't use the
+@code{raggedright} option.