This is the maximum number of digits the caller is allowed to enter as a single input. For example, you may want this to be 4 to be able to accept as input the digit sequences 1001 to 1019, corresponding to "Local_Extension" registered phones in the demo dialplan. The caller will be allowed to enter shorter digit sequences by terminating the sequence using "confirm-key" (usually #), or by waiting for "inter-digit-timeout."