The overall range of calendar dates and times over which this schedule is active. It is stored in a slightly extended version of the format for a 'period-explicit' defined in RFC 2445. This format is expressed as a string representing the starting date and time, in which the character 'T' indicates the beginning of the time portion, followed by the solidus character, '/', followed by a similar string representing an end date and time. The start of the period MUST be before the end of the period. Date-Time values are expressed as substrings of the form 'yyyymmddThhmmss'. For example: 20000101T080000/20000131T130000 January 1, 2000, 0800 through January 31, 2000, 1PM The 'Date with UTC time' format defined in RFC 2445 in which the Date-Time string ends with the character 'Z' is not allowed. This 'period-explicit' format is also extended to allow two special cases in which one of the Date-Time strings is replaced with a special string defined in RFC 2445: 1. If the first Date-Time value is replaced with the string 'THISANDPRIOR', then the value indicates that the schedule is active at any time prior to the Date-Time that appears after the '/'. 2. If the second Date-Time is replaced with the string 'THISANDFUTURE', then the value indicates that the schedule is active at any time after the Date-Time that appears before the '/'. Note that although RFC 2445 defines these two strings, they are not specified for use in the 'period-explicit' format. The use of these strings represents an extension to the 'period-explicit' format.