(time-now)
Returns a time expression for the current time.

(make-time DATE)
Returns a time expression for the given date, which should be formatted as an ISO 8601 date/time.

(time-add-day TIME N)
Add N days to TIME, and return the new date.

(time-day-begin)
Return a time expression of the start of the day.

(time-day-end)
Return a time expression of the end of the day.

(uid? UID)
Returns a boolean indicating whether the component has the given UID.

(occur-in-time-range? START END)
Returns a boolean indicating whether the component has any occurrences in the specified time range.

(contains? FIELD STR)
Returns a boolean indicating whether the specified field in the component contains the specified string.  Valid fields: any, comment, description, summary, location.

(has-alarms?)
Returns a boolean indicating whether the component has any alarms.

(has-alarms-in-range? START END)
Returns a boolean indicating whether the component has alarms in the given time range or not.

(has-recurrences?)
Returns a boolean indicating whether the component has any recurrences.

(has-categories? STR+)
Returns a boolean indicating whether the component has all of the specified categories.

(has-categories? #f)
Returns a boolean indicating if the component has no categories.

(is-completed?)
Returns a boolean indicating whether the component is completed.  This is really only useful for TODO components.

(completed-before? TIME)
Returns a boolean indicating whether the component was completed on or before the given time. This is really only useful for TODO components.