Each instance of the system class
sql-expression-object represents a SQL expression. They can be used inside another instance of
sql-expression-object, in a "[...]" syntax expression or as arguments to the Common SQL functions. They are created by the "[...]" syntax (see Enclosing database identifiers) or dynamically by sql-expression or string-prefix-with-n-if-needed.
LispWorks User Guide and Reference Manual - 20 Sep 2017