Entry is the link in the linked list of all entries.
Scope the entry belongs to.
Entries are accessed by type, and entries with different types never mix
Running cancel, will remove the entry from the stored list and it will be no longer available
If entry is already cancelled, nothing happens.
Returns Doc object, loaded with property names and values describing this instance
Returns true is the entry is already cancelled.
tag returns this instance String representation, which should be used insted of toString
Value is entry's pay load. It can be anything.