/**
 * @anchor modules_anchor
 *
 * @defgroup constructs C++ Constructs Used by All Modules
 * \brief These are C++ constructs defined by the modules.
 *
 * @defgroup constants Constants
 * @brief Constants you can change
 *
 * @defgroup utils Utils
 * @brief The utils directory is for various programs and scripts related 
 * to code coverage, test suites, style checking, and benchmarking.
 *
 * @defgroup core Core
 * \brief The "core" module contains:
 *    - a time management class to hold a time and convert between various time units: ns3::Time 
 *    - a scheduler base class used to implement new simulation event schedulers:       
 *      ns3::Scheduler and ns3::SchedulerFactory 
 *    - a simulator class used to create, schedule and cancel events: ns3::Simulator
 *    - a Functor class: ns3::Callback  
 *    - an os-independent interface to get access to the elapsed wall clock time: ns3::SystemWallClockMs 
 *    - a class to register regression tests with the test manager: ns3::Test and ns3::TestManager
 *    - debugging facilities: \ref logging, \ref assert
 *    - \ref randomvariable
 *    - a base class for objects which need to support per-instance "attributes" and
 *      trace sources: ns3::ObjectBase
 *    - a base class for objects which need to support reference counting
 *      and dynamic object aggregation: ns3::Object
 *    - a smart-pointer class ns3::Ptr designed to work together with ns3::Object
 *    - a configuration class used to set and control all attributes and trace sources
 *      in a simulation: ns3::Config.
 *
 */