* lily/parser.yy (Simple_music): add \applyoutput, syntax

[lilypond.git] / lily / item.cc

diff --git a/lily/item.cc b/lily/item.cc
index c3e8c38569187870043919a3aa1242eed2de241f..236885dc328f8db57e8999cad82c8cfdfc42910f 100644 (file)
--- a/lily/item.cc
+++ b/lily/item.cc
@@ -193,12 +193,25 @@ unsmob_item (SCM s )
 
 ADD_INTERFACE(Item,
              "item-interface",
-             "
-
-Grobs can be distinguished in their role in the horizontal spacing.
-Many grobs define constraints on the spacing by their sizes. For
-example, note heads, clefs, stems, and all other symbols with a fixed
-shape.  These grobs form a subtype called @code{Item}.
-
-",
+             "\n"
+             "\n"
+             "Grobs can be distinguished in their role in the horizontal spacing.\n"
+             "Many grobs define constraints on the spacing by their sizes. For\n"
+             "example, note heads, clefs, stems, and all other symbols with a fixed\n"
+             "shape.  These grobs form a subtype called @code{Item}.\n"
+             "\n"
+             "\n"
+             "Some items need special treatment for line breaking. For example, a\n"
+             "clef is normally only printed at the start of a line (i.e. after a\n"
+             "line break).  To model this, `breakable' items (clef, key signature,\n"
+             "bar lines, etc.) are copied twice. Then we have three versions of each\n"
+             "breakable item: one version if there is no line break, one version\n"
+             "that is printed before the line break (at the end of a system), one\n"
+             "version that is printed after the line break.\n"
+             "\n"
+             "Whether these versions are visible and take up space, is determined by\n"
+             "the outcome of the @code{break-visibility}. This grob property is a\n"
+             "function taking a direction (-1, 0 or 1) as argument. It returns a\n"
+             "cons of booleans, signifying whether this grob should be transparent\n"
+             "and have no extent.\n",
              "no-spacing-rods break-visibility breakable")