Persistent symbols created in the "KernelSession" location disappear when the kernel quits:

Persistent symbols created in the "FrontEndSession" location survive a kernel restart:

These symbols disappear when the front end is restarted:

Persistent symbols in the "Local" location are stored in a file in your account:

These symbols are stored under the $LocalBase directory and remain indefinitely:

Modify values of persistent symbols:

Modify list values:

Modify parts of list values:

Modify association values:

Modify elements of association values:

Define a persistent value that expires at the beginning of the year 2020:

Verify the expiration date of the underlying persistent object:

Define a persistent value that expires at the beginning of next year:

Verify the expiration date of the underlying persistent object:

Create a complement of persistent values with key "lval" at various locations:

List all existing values for the key "lval" on $PersistencePath:

By default, only the first value is returned:

Join and flatten all sublists:

Join all sublists:

Create a complement of persistent associations with name "aval" at various locations:

List all existing values on $PersistencePath:

Merge the values of identical keys in the associations:

Define a default value for "mylist" with a custom merging function:

Define additional values at different persistence locations:

For looking up values, the custom merging function is now used:

Define a persistent value that expires in 5 seconds:

After 5 seconds, it is no longer used:

Define a persistent object that expires in 5 days:

Verify the expiration date of the underlying persistent object:

Define a value preprocessing function that accepts only integers:

Set up a default value and the value preprocessing function for a persistent value named "int":

Assign an integer at any persistence location:

Assigning anything else generates an error, and the assignment is not performed: