/*!
\page plug_page_front Plug: Plugin Framework
\if ( PIXAR_MFB_BUILD )
\mainpage  Plug: Plugin Framework
\publicLib
\endif


\section Overview

Provides a plug-in framework implementation.  The PlugPlugin class defines the
interface to plug-in modules.  The PlugRegistry class defines a mechanism for
discovering and registering plug-in modules both automatically upon first use
and manually at run-time by client calls to PlugRegistry::RegisterPlugins.
PlugRegistry sends the PlugNotice::DidRegisterPlugins notice when new plug-ins
are registered (both when Plug is first used and again for subsequent calls to
PlugRegistry::RegisterPlugins).

PlugRegistry also provides a mechanism to find TfType objects for types defined
in plug-ins, then find the plug-ins that provide those types, and read metadata
related to those plug-ins and the contained types, and load the plug-ins.

The PlugPlugin class contains properties that indicate whether or not a plug-in
is currently loaded and whether a plug-in is a Python module or a C++ shared
library.  It also includes functions that return a plug-in's name, location in
the file system, the names of its base classes, its metadata, and any existing
dependencies.

\section Plug_Discovery Plug-In Discovery & Registration

The PlugRegistry class discovers plug-ins both on first use and in response to
calls to PlugRegistry::RegisterPlugins.  This means that plugin-dependent code
should listen to the PlugNotice::DidRegisterPlugins notification in order to
update appropriately if new plugins are registered during the course of a
running program.

\section Usage

For information on how to add concrete plug-in types to applications like
Presto, see the API documentation for the libraries that implement functionality
for those types of components.  For example, the Mf library includes functions
for registering prim plug-ins; the Wd library includes functions for registering
GUI components such as editor plug-ins.

\section Plug-In Metadata

Plug-ins are found and described using plugInfo.json files that may be read
without loading the plugin.  The structure of a plugInfo.json file is described
in detail in the \ref plug_plugInfo "PlugRegistry class".


*/