=head1 Section 1: The Moosic Server's Data Model

This section describes, in precise terms, the data objects that can be accessed
and manipulated by sending requests to the Moosic server.

=over

=item song queue

This is the foremost data object maintained by the Moosic server. It is an
ordered sequence of strings that represents the queue of songs that are waiting
to be played.  Each item in this list identifies a song that will be played by
the Moosic server.  Usually, these items are the names of files on disk that
contain each song, but this does not have to be the case.  For instance, an HTTP
URL might be used to name a song if a program that can play songs from the Web
is appropriately registered with the Moosic server (see "player configuration"
later in this section).

=item current song

This is a string that identifies the song that is currently being played by the
Moosic server.  If nothing is currently playing, then this will be the empty
string.

=item queue running flag

This is a boolean value that indicates whether the Moosic server will start
playing a new song as soon as the current song has finished and the song queue
is not empty.

=item pause flag

This is a boolean value that indicates whether the current song is paused or
not.

=item loop mode flag

This is a boolean value that sets "loop mode".  When loop mode is on, songs are
returned to the end of the song queue when they finish playing instead of being
discarded.

=item history

This is a list of songs that the Moosic server has finished playing.  Note that
songs named in this list may have finished playing early at the request of a
user (i.e. through use of the "next" command).  Each entry in this list is
actually a 3-tuple of (song, start time, finish time).

=item maximum history size

This is the maximum number of songs that will be stored in the history list.
Old entries are removed from the history to make room for newer entries when
this limit is reached.

=item player configuration

This is an ordered mapping that associates regular expressions (text patterns)
to programs.  For each regular expression, the associated program is expected to
be able to play any queue items that match that regular expression.  Each
program is a list in which the name of the executable file that contains the
program is the first element and the program's arguments are the rest of the
elements.

=item last queue update

This is the time at which the song queue was last modified.  It a floating-point
number that represents time as the number of seconds since the epoch.

=item server version

This is a string that describes the version of the program that implements the
Moosic server.  It has no specific, well-defined semantics.

=item API version

This is a pair of integers, one representing the "major" version, and the other
representing the "minor" version.  These numbers are meant to provide some
useful compatibility information to Moosic clients.  As this API changes, these
numbers will change in the following ways.  If the API has been changed in a
backward-compatible way (e.g. a new method was added or an existing method was
overloaded), then the minor version will increase and the major version will
remain unchanged.  However, if the API has been changed in such a way that
existing code that uses the API might break (e.g.  a method was removed or its
return value or parameter types were changed), then the major version will
increase and the minor version may be reset to any value (although it will
usually be reset zero).

=back