The MitreLimit property defines the maximum limit for the miter tip of a line that has its Joins set to Mitred. If the mitered join exceeds the defined limit, the join is beveled at the limit.
Typically you would set the MitreLimit on the Polyline Properties window and would not animate it. However, you can animate the MitreLimit if required. You can animate the limit so that it is a certain number by entering the relevant number for its expression. Alternatively, you can animate it so that the limit changes size according to the value or state of an item in the database.
For example:
IIF( ".1 Bit Digital.AlarmState" = 4, 13.50, 10.00 )
This means that when the point named '1 Bit Digital' has an alarm state of 4 (an unacknowledged alarm), the MitreLimit is 13.50 pt. When the point has any other alarm state, the MitreLimit is 10.00 pt.