code: static public void put(String key, Object o) {
          if (setContext()) {
              m_context.put(key, o);
          } else {
              m_defaultContext.put(key, o);
          }
      }
docs: Put a context value (the <code>o</code> parameter) as identified
  with the <code>key</code> parameter into the current thread's
  context map.
  
  <p>If the current thread does not have a context map it is
  created as a side effect.