More docs.

doc/sql.extensions/README.iif

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+--------------------
+IIF builtin function
+--------------------
+
+Function:
+    Return a value of the first sub-expression if the given search condition
+    evaluates to TRUE, otherwise return a value of the second sub-expression.
+
+Author:
+    Oleg Loa <loa@mail.ru>
+
+Format:
+    IIF ( <search condition>, <value expression>, <value expression> )
+
+Syntax Rule(s):
+    IIF (SC, V1, V2) is equivalent to the following <case specification>:
+         CASE WHEN SC THEN V1 ELSE V2 END
+
+Example(s):
+    SELECT IIF(VAL > 0, VAL, -VAL) FROM OPERATION