Special properties provide an alternative access method to Org-mode features, like the TODO state or the priority of an entry, discussed in the previous chapters. This interface exists so that you can include these states in a column view (see Column view), or to use them in queries. The following property names are special and should not be used as keys in the properties drawer:
TODO The TODO keyword of the entry.
TAGS The tags defined directly in the headline.
ALLTAGS All tags, including inherited ones.
CATEGORY The category of an entry.
PRIORITY The priority of the entry, a string with a single letter.
DEADLINE The deadline time string, without the angular brackets.
SCHEDULED The scheduling timestamp, without the angular brackets.
CLOSED When was this entry closed?
TIMESTAMP The first keyword-less timestamp in the entry.
TIMESTAMP_IA The first inactive timestamp in the entry.
CLOCKSUM The sum of CLOCK intervals in the subtree. org-clock-sum
must be run first to compute the values.
BLOCKED "t" if task is currently blocked by children or siblings
ITEM The content of the entry.