4. The method according to claim 2 , where setting the target length as the defined target length that corresponds to the defined duration of time for which the user-maintained press of the input key that enters the symbol of the sub-sequence was detected comprises: setting the target length to a corresponding target length defined to correspond to a measured selection time of a last symbol of the sub-sequence; and where enabling user selection of one of the eligible strings via the user input device as the target string comprises: displaying the eligible strings; prompting the user to select one of the eligible strings; detecting a selection of an eligible string; and completing the sub-sequence automatically in response to detecting the selection of the eligible string.
4. The method according to claim 2 , where setting the target length as the defined target length that corresponds to the defined duration of time for which the user-maintained press of the input key that enters the symbol of the sub-sequence was detected comprises: setting the target length to a corresponding target length defined to correspond to a measured selection time of a last symbol of the sub-sequence; and where enabling user selection of one of the eligible strings via the user input device as the target string comprises: displaying the eligible strings; prompting the user to select one of the eligible strings; detecting a selection of an eligible string; and completing the sub-sequence automatically in response to detecting the selection of the eligible string. 5. The method according to claim 4 , further comprising: detecting a selection via the user input device of a user interface button indicating a change of the target length of the target string; and updating the target length based upon the indicated change of the target length of the target string.