How we can write code in custom.pll in r12 to control the events on button?

How can print report by tools menu for custom form by Custom.pll ?

need all steps please.

Here are some notes on Custom Library.

1. You cannot change specifications of CUSTOM package. 

2. You cannot use SQL in CUSTOM.pll instead call stored procedures. 

3. Do not use APP_ITEM_PROPERTY instead use SET_ITEM_PROPERTY. 

4. You have to go completely out of browser, exit the browser. 

5. Make a backup of original CUSTOM.pll 

6. CUSTOM.pll cannot be generated using Form Designer it has to de done using Form Generator. 

7. Make sure you use else null as last exception to all IF condition. 

8. Function name are described in Application Developer or Sys admin under Forms-Function. 

9. Be careful when you write FUNCTION_NAME i.e. make sure the spelling is correct.

 Things you can do with CUSTOM.pll 

1. Make an item view only 

2. Make an item updateable 

3. Make an item hidden 

4. Highlight an item. 

5. Change/Disable Button, Tabs. 

6. Text to be entered only in Caps. 

7. Change of navigation. 

8. Change the size and position of fields 

9. Change the prompt. 

10. Change the LOV