= Tab display

        TAB {on | off | clear | nn}
            on      :display tab char and DBCS(japanese) space.
                     Char used to display tab and its following space
                     is customaizable by .INI file parameter.
                     Default is Tab       :Up-arrow
                                Tab-skip  :Right arrow
                                DBCS space:shadow box
            off     :tab char is not displayed.
                     Special char for un-displayable char
                     is alaways displayed regardless this option.
            clear   :remove tab with space remained.
            nn      :Tab column interval,default is 4.
                     Tab key cause cursor jump not to next tab column
                     but jump to next field when tab column is 0.
                     Maximum 12.