Variables Description
attr scans the request, session, and application attributes, in that order
request request attributes
session session attributes
application application attributes
parameters request params
Defining Java Constant Variables Description
ActionContext.PARAMETERS com.opensymphony.xwork.ActionContext.parameters Same as 'parameters' above
ActionContext.SESSION com.opensymphony.xwork.ActionContext.session Same as 'session' above
ActionContext.APPLICATION com.opensymphony.xwork.ActionContext.application Same as 'application' above
ActionContext.LOCALE com.opensymphony.xwork.ActionContext.locale From locale defined in webwork.properties else from the request object
ActionContext.DEV_MODE __devMode true or false if in development mode or otherwise whereby resource bundle webwork.properties, xwork.xml, converters, validators will be refreshed when changes
ActionContext.HTTP_REQUEST com.opensymphony.xwork.dispatcher.HttpServletRequest Same as 'request' above
ActionContext.HTTP_RESPONSE com.opensymphony.xwork.dispatcher.HttpServletResponse Same as 'response' above
ActionContext.SERVLET_CONTEXT com.opensymphony.xwork.dispatcher.ServletContext Servlet's spec's ServletContext object
ActionContext.COMPONENT_MANAGER com.opensymphony.xwork.interceptor.component.ComponentManager Webwork's IOC component manager

For further information
@see com.opensymphony.webwork.dispatcher.DispatcherUtils#createContextMap
@see com.opensymphony.xwork.interceptor.component.ComponentInterceptor
@see com.opensymphony.webwork.WebWorkStatics