this referent is used in a
repeat over referents loop to refer to the current referent.
this referent can be used in many ways:
using referentprefix, wherever a string expression is expected. The current value of the selected referent is returned.
set this referent to).
key of this referent). The selected referent is guaranteed to have a key (unlike integers, streams and shelves) because it must exist, and all referents have a key.
this referent (is | isnt) attached). The test succeeds if the selected referent has been opened or defined (with the
setaction, for example) at some time.