+Within this directory the two interesting subdirectories are
+
+@itemize
+
+@item @file{../ly/} - contains files in LilyPond format
+
+@item @file{../scm/} - contains files in Scheme format
+
+@end itemize
+
+Let's begin by looking at some files in @file{../ly/}.
+Open @file{../ly/property-init.ly} in a text editor. The one
+you normally use for @code{.ly} files will be fine. This file
+contains the definitions of all the standard LilyPond built-in
+commands -- like @code{\stemUp} and @code{\slurDotted}. You will
+see that these are nothing more than definitions of variables
+containing one or a group of @code{\override} commands. For
+example, @code{/tieDotted} is defined to be:
+
+@example
+tieDotted = @{
+ \override Tie #'dash-period = #0.75
+ \override Tie #'dash-fraction = #0.1
+@}
+@end example
+
+If you do not like the default values these built-in commands can
+be redefined easily, just like any other variable, at the
+head of your input file.
+
+These are the most useful files to be found in @file{../ly/}:
+
+@multitable @columnfractions .4 .6
+@headitem Filename
+ @tab Contents
+@item @file{../ly/engraver-init.ly}
+ @tab Definitions of engraver Contexts
+@item @file{../ly/paper-defaults.ly}
+ @tab Specifications of paper-related defaults
+@item @file{../ly/performer-init.ly}
+ @tab Definitions of performer Contexts
+@item @file{../ly/property-init.ly}
+ @tab Definitions of all common macros
+@end multitable
+
+Other settings (such as the definitions of markup commands) are
+stored as @code{.scm} (Scheme) files. The Scheme programming
+language is used to provide a programmable interface into
+LilyPond internal operation. Further explanation of these files
+is currently outside the scope of this manual, as a knowledge of
+the Scheme language is required. Users should be warned that
+a substantial amount of technical knowledge or time is required
+to understand Scheme and these files.
+
+If you have this knowledge, the Scheme files which may be of
+interest are:
+
+@multitable @columnfractions .4 .6
+@headitem Filename
+ @tab Contents
+@item @file{../scm/auto-beam.scm}
+ @tab Sub-beaming defaults
+@item @file{../scm/define-grobs.scm}
+ @tab Default settings for grob properties
+@item @file{../scm/define-markup-commands.scm}
+ @tab Specify all markup commands
+@item @file{../scm/midi.scm}
+ @tab Default settings for MIDI output
+@item @file{../scm/output-lib.scm}
+ @tab Settings that affect appearance of frets, colors,
+ accidentals, bar lines, etc
+@item @file{../scm/parser-clef.scm}
+ @tab Definitions of supported clefs
+@item @file{../scm/script.scm}
+ @tab Default settings for articulations
+@end multitable
+