diff b/w POST-TEXT-ITEM and WHEN-VALIDATE-ITEM?

This Question is for diff b/w POST-TEXT-ITEM and WHEN-VALIDATE-ITEM?
Suppose you have two fields 'A' and 'B'
A will Have initial value --> 100
Now u want go to change the Value of A to ---> 200 (WVI will be fire)It will not give any error
And in When Validate Item u give a condition ---> If a<500 p="p">And u r assigning the value to 'A' in POST-TEXT-ITEM --> now the POST-TEXT-ITEm will fire and the value of 'A' should be change to 700.

Now the Question is WHEN-VALIDATE-ITEM will raise error or not?
Yes, It will fire and it will give an error message. for when validate item there is no need to change the value if it is change as internally then also WHEN-VALIDATE-ITEM will fire.

Question:  Why are PL/SQL ref cursors important to PL/SQL performance?

Answer: The ref cursor is a "pointer" data types that allows you to quickly reference any cursor result (usually an internal PL/SQL table array) with data values kept in super-fast RAM.

Definition of a ref cursor
The name "ref cursor" can be confusing because a ref cursor variable is not a cursor, but a variable that points to a cursor.  In essence, a ref cursor allows you to store the result of a "bulk collect" from a table (or any PL/SQL cursor return set) into a PL/SQL table (RAM array) and then reference the array with the ref cursor as a pointer.  Here is a simple example of using a ref cursor.

Once you load a PL/SQL table (an in-RAM array), a ref cursor allows you to reference the array within your PL/SQL code without having to pass the array to a new procedure or function.  Instead of passing the "baggage" of the actual RAM array, you simple pass the ref cursor, which points to the array values.