CalendarExpression
date: YYYY.MM.DD
weekdays: [1-7]{1,7}
periode: /begin:date-end:date/
weekdays_in_periode: periode weekdays
calendar: date|periode|weekdays_in_periode
operators:
union: +
difference: -
calendar expression: calendar [operator calendar]...
exemple:
/2012.01.01-2013.01.01/1357+/2012.12.31-2013.04.01/+2013.05.01-2013.01.01