calscale:
    purpose: This property defines the calendar scale used for the calendar information specified in the calendar object.
    constant_value: GREGORIAN
    rfc_ref: "4.7.1 p 73"
method:
    purpose: This property defines the iCalendar object method associated with the calendar object
    ruby_name: icalendar_method
    rfc_ref: "4.7.2 p 74-75"
prodid:
    purpose: This property specifies the identifier for the product that created the iCalendar object.
    required: true
    default_value: '-//com.denhaven2/NONSGML ri_cal gem//EN'
    rfc_ref: '4.7.3 pp 75-76'    
version:
    purpose: This property specifies the identifier corresponding to thehighest version number or the minimum and maximum range of the iCalendar specification that is required in order to interpret the iCalendar object.
    constant_value: '2.0'
    rfc_ref: '4.7.4 pp 76-77'    
attach:
    purpose: The property provides the capability to associate a document object with a calendar component.
    type: Uri
    rfc_ref: '4.8.1.1 pp 77-78'
categories:
    purpose: This property defines the categories for a calendar component.
    type: Array
    array_type: Text
    rfc_ref: '4.8.1.2 pp 78-79'
class:
    ruby_name: security_class
    purpose: This property defines the access classification for a calendar component.
    rfc_ref: '4.8.1.3 pp 79-80'   
comment:
    purpose: This property specifies non-processing information intended to provide a comment to the calendar user.
    rfc_ref: '4.8.1.4 pp 80-81'
description:
    purpose: This property provides a more complete description of the calendar component, than that provided by the "SUMMARY" property.
    rfc_ref: '4.8.1.5 pp 81-82'
geo:
    purpose: This property specifies information related to the global position for the activity specified by a calendar component.
    type: Geo
    rfc_ref: '4.8.1.6 pp 82-83'
location:
    purpose: This property defines the intended venue for the activity defined by a calendar component.
    rfc_ref: '4.8.1.7 pp 84'
percent-complete:
    purpose: This property is used by an assignee or delegatee of a to-do to convey the percent completion of a to-do to the Organizer.
    type: Integer
    rfc_ref: '4.8.1.8 pp 85'
priority:
    type: Integer
    purpose: This property defines the relative priority for a calendar component.
    rfc_ref: '4.8.1.9 pp 85-87'
resources:
    purpose: This property defines the equipment or resources anticipated for an activity specified by a calendar entity.
    type: 'Array'
    rfc_ref: '4.8.1.10 pp 87-88'
status:
    purpose: This property defines a short summary or subject for the calendar component.
    rfc_ref: '4.8.1.11 pp 80-89'
summary:
    purpose: This property defines a short summary or subject for the calendar component.
    rfc_ref: '4.8.1.12 pp 89-90'
completed:
    purpose: This property specifies the date and time that a to-do was actually completed.
    type: DateTime
    type_constraint: must_be_utc
    rfc_ref: '4.8.2.1 pp 90-91'
dtend:
    purpose: This property specifies the date and time that a calendar component ends.
    type: date_time_or_date
    rfc_ref: '4.8.2.2 pp 91-92'
due:
    purpose: This property defines the date and time that a to-do is expected to be completed.
    type: date_time_or_date
    rfc_ref: '4.8.2.3 pp 92-93'
dtstart: 
    purpose: This property specifies when the calendar component begins.
    type: date_time_or_date
    rfc_ref: '4.8.2.4 pp 93-94'
duration:
    purpose: This property specifies a positive duration of time.
    type: Duration
    rfc_ref: '4.8.2.5 pp 94-95'
freebusy:
    purpose: This property defines one or more free or busy time intervals.
    type: Period
    type_constraint: must_be_utc
    rfc_ref: '4.8.2.6 pp 95-96'
transp:
    purpose: This property defines whether an event is transparent or not to busy time searches.
    rfc_ref: '4.8.2.7 pp 96-97'
tzid:
    purpose: This property specifies the text value that uniquely indentifies the "VTIMEZONE" calendar component.
    rfc_ref: '4.8.3.1 pp 97-98'
tzname:
    purpose: This property specifies the customary designation for a time zone description.
    rfc_ref: '4.8.3.2 p 99'
tzoffsetfrom:
    purpose: This property specifies the offset which is in use prior to this time zone observance
    type: UtcOffset
    rfc_ref: '4.8.3.3 pp 99-100'
tzoffsetto:
    purpose: This property specifies the offset which is in use in this time zone observance
    type: UtcOffset
    rfc_ref: '4.8.3.4 pp 100-101'
tzurl:
    purpose: The TZURL provies a means for a VTIMEZONE component to point to a network location that can be used to retrieve an up-to_date version of itself.
    type: Uri
    rfc_ref: '4.8.3.4 p 101'    
attendee:
    purpose: The property defines an 'Attendee' within a calendar component.
    type: CalAddress
    rfc_ref: '4.8.4.1 pp 102-104'   
contact:
    purpose: The property is used to represent contact information oralternately a reference to contact information associated with the calendar component.
    rfc_ref: '4.8.4.2 pp 104-106'   
organizer:
    purpose: The property defines the organizer for a calendar component.
    type: CalAddress
    rfc_ref: '4.8.4.3 pp 106-107'   
recurrence-id:
    purpose: This property is used in conjunction with the "UID" and "SEQUENCE" property to identify a specific instance of a recurring "VEVENT", "VTODO" or "VJOURNAL" calendar component. The property value is the effective value of the "DTSTART" property of the recurrence instance.
    type: date_time_or_date
    rfc_ref: '4.8.4.4 pp 107-109'   
related-to:
    purpose: The property is used to represent a relationship or reference between one calendar component and another.
    rfc_ref: '4.8.4.5 pp 109-110'   
url:
    purpose: This property defines a Uniform Resource Locator (URL) associated with the iCalendar object.
    type: Uri
    rfc_ref: '4.8.4.6 pp 110-111'   
uid:
    purpose: This property defines the persistent, globally unique identifier for the calendar component.
    rfc_ref: '4.8.4.7 pp 111-112'   
exdate:
    purpose: This property defines the list of date/time exceptions for a recurring calendar component.
    type: 'OccurrenceList'
    rfc_ref: '4.8.5.1 pp 112-114'   
exrule:
    purpose: This property defines a rule or repeating pattern for an exception to a recurrence set.
    type: 'RecurrenceRule'
    rfc_ref: '4.8.5.2 pp 114-125'   
rdate:
    purpose: This property defines the list of date/times for a recurring calendar component.
    type: 'OccurrenceList'
    rfc_ref: '4.8.5.3 pp 115-117'   
rrule:
    purpose: This property defines a rule or repeating pattern for recurring events, to-dos, or time zone definitions.
    type: 'RecurrenceRule'
    rfc_ref: '4.8.5.4 pp 117-125'
action:
    purpose: This property defines the action to be invoked when an alarm is triggered
    rfc_ref: '4.8.6.1 p 126'
repeat:
    purpose: This property defines the number of times the alarm should be repeated, after the initial trigger.
    type: Integer
    rfc_ref: '4.8.6.2 p 126-127'
trigger:
    purpose: This property specifies when an alarm will trigger.
    type: Duration
    rfc_ref: '4.8.6.3 p 127-129'
created:
    purpose: This property specifies the date and time that the calendar information was created by teh calendar user agent in the calendar store.
    type: DateTime
    rfc_ref: '4.8.7.1 pp 129-130'   
dtstamp:
    purpose: This property indicates the date/time that the instance of the iCalendar object was created.
    type: DateTime
    auto_set: to_ical
    rfc_ref: '4.8.7.2 pp 130-131'   
last-modified:
    purpose: This property specifies the date and time that the information associated with the calendar component was last revised in teh calendar store.
    type: DateTime
    rfc_ref: '4.8.7.3 p 131'   
sequence:
    purpose: This property defines the revision sequence number of the calendar component within a sequence of revisions.
    type: Integer
    auto_set: sequence_modifiers
    rfc_ref: '4.8.7.4 pp 131-133'   
request-status:
    rfc_ref: '4.8.8.2 pp 134-136'