 The text editing environment in <unk> uses a double space following a period to identify the end of sentences unambiguously ; the double space convention prevents confusion with periods within sentences that signify abbreviations . How <unk> recognizes the end of a sentence is controlled by the settings sentence @-@ end @-@ double @-@ space and sentence @-@ end . The vi editor also follows this convention ; thus , it is relatively easy to manipulate ( jump over , copy , <unk> ) whole sentences in both <unk> and vi . 
