+ /* ES TODO: cause can't be Music*/
+ if (Music *m = unsmob_music (cause))
+ m->origin ()->message (s);
+ else if (Stream_event *ev = unsmob_stream_event (cause))
+ ev->origin ()->warning (s);
+ else
+ ::message (s);
+}
+
+
+ADD_INTERFACE (Grob,
+ "A grob represents a piece of music notation\n"
+ "\n"
+ "All grobs have an X and Y-position on the page. These X and Y positions\n"
+ "are stored in a relative format, so they can easily be combined by\n"
+ "stacking them, hanging one grob to the side of another, and coupling\n"
+ "them into a grouping objects.\n"
+ "\n"
+ "Each grob has a reference point (a.k.a. parent): the position of a grob\n"
+ "is stored relative to that reference point. For example the X-reference\n"
+ "point of a staccato dot usually is the note head that it applies\n"
+ "to. When the note head is moved, the staccato dot moves along\n"
+ "automatically.\n"
+ "\n"
+ "A grob is often associated with a symbol, but some grobs do not print\n"
+ "any symbols. They take care of grouping objects. For example, there is a\n"
+ "separate grob that stacks staves vertically. The @ref{NoteCollision}\n"
+ "is also an abstract grob: it only moves around chords, but doesn't print\n"
+ "anything.\n"
+ "\n"
+ "Grobs have a properties: Scheme variables, that can be read and set. "
+ "They have two types. Immutable variables "
+ "define the default style and behavior. They are shared between many objects. "
+ "They can be changed using @code{\\override} and @code{\\revert}. "
+ "\n\n"
+ "Mutable properties are variables that are specific to one grob. Typically, "
+ "lists of other objects, or results from computations are stored in"
+ "mutable properties: every call to set-grob-property (or its C++ equivalent) "
+ "sets a mutable property. "
+ "\n\n"
+ "The properties @code{after-line-breaking} and @code{before-line-breaking} "
+ "are dummies that are not user-serviceable. "
+
+ ,
+
+ /* properties */
+ "X-extent "
+ "X-offset "
+ "Y-extent "
+ "Y-offset "
+ "after-line-breaking "
+ "avoid-slur "
+ "axis-group-parent-X "
+ "axis-group-parent-Y "
+ "before-line-breaking "
+ "cause "
+ "color "
+ "extra-X-extent "
+ "extra-Y-extent "
+ "extra-offset "
+ "interfaces "
+ "layer "
+ "meta "
+ "minimum-X-extent "
+ "minimum-Y-extent "
+ "outside-staff-horizontal-padding "
+ "outside-staff-padding "
+ "outside-staff-priority "
+ "rotation "
+ "springs-and-rods "
+ "staff-symbol "
+ "stencil "
+ "transparent "
+ );
+
+/****************************************************************
+ CALLBACKS
+****************************************************************/
+
+static SCM
+grob_stencil_extent (Grob *me, Axis a)
+{
+ Stencil *m = me->get_stencil ();
+ Interval e;
+ if (m)
+ e = m->extent (a);
+ return ly_interval2scm (e);
+}