Comment 2 for bug 1412635

Sample:

ask0:
    action: ....
    publish:
        x: $.....

task1:
    action: foo param={$.global_var} # returns {x:y}
    publish:
        p1: {$.global_var} + {$.x} # local variable, input of action, overrides the global x
        p11: {$.global_var} +{$.__global.x} # explicitly refer to x from global
        p12: {$.global_var} +{$.__action.x} # explicitly refer to x from action
        p2: {$.global_var} + {$.__task.task1.x}

task2:
    action: bar param = {$.__task.task1.x}
    action: bar param = {$.x}

alternative names
1) pointing to the incoming global context:
__wf
__wf_ctx
__ctx
__global

2) pointing to action output of this very task
* __action
* __self
* __result
* __res
* __raw
* __raw_result