# $Id$
#
# >>Copyright::
# Copyright (c) 1992-1996, Ian Clatworthy (ianc@mincom.com).
# You may distribute under the terms specified in the LICENSE file.
#
# >>History::
# -----------------------------------------------------------------------
# Date      Who     Change
# 29-Feb-96 ianc    SDF 2.000
# -----------------------------------------------------------------------
#

H1: Modules and Libraries

H2: Modules

[[SDF]] can be extended by using {{modules}}. A module is a normal
[[SDF]] file which typically contains reusable entities like {{macros}},
{{filters}} and {{styles}}. Modules are loaded by the {{MAC:use}}
macro. For example:

E:   !use "delphi"

By convention, modules are given the {{sdm}} extension. The {{MAC:use}}
macro adds this extension if none is provided. Modules can also be
loaded by using {{CMD:sdf}}'s -u option.

H2: Libraries

A collection of related modules can be placed into a {{library}}
which is simply a subdirectory under the {{sdf/home}} directory on
Perl's library path.
Libraries can be loaded by the {{MAC:inherit}} macro which
essentially does the following:

^ appends the matching directory onto the {{include path}}
+ loads the matching {{main module}}.

For example:

E:   !inherit "images"

^ appends sdf/home/images onto the include path
+ loads the sdf/home/images/images.sdm module.

H2: The Configuration Library

After loading the standard library ({{stdlib}}), [[SDF]] loads
the configuration library, if any. This is typically specified
via the {{VAR:OPT_CONFIG}} variable being initialised on the top
line of the file via the {{MAC:init}} macro. It can also be set via
{{CMD:sdf}}'s -c option.

While {{CMD:sdf}} only supports a single configuration library,
additonal libraries can be loaded via the {{MAC:inherit}} macro.
Furthermore, a library can inherit things from other libraries,
making it easy to create new ones.