pragmas in doubly linked lists

["L. B." <mario.blunk.gplus@gmail.com>]

Hello,

I'm having issues with cursors of doubly linked lists (erroneous memory access exceptions).
So I'm wondering whether the pragmas might solve the problems. What is the purpose of the pragmas defined in the package like

pragma Preelaborate(Doubly_Linked_Lists);
pragma Preelaborable_Initialization(List);
pragma Preelaborable_Initialization(Cursor);

What are they good for and how to use them ? Some simple examples would be very helpful. Thank you.