regading the class cl_powl_table_helper

In class  cl_powl_table_helper while crating the object to this class it is triggering the constructoras with i_model shown below

data b type ref to CL_POWL_TABLE_HELPER.

CREATE OBJECT b

EXPORTING

    i_model = ?

    i_root_node = wd_context

  .How to get or from where i get i_model in above constructor.