This Auto Expand Panels script operates as follows:

1. Class Initialization: The script is encapsulated within a PHP class named Expand_Sidebar_Panels_On_Mutation.

2. WordPress Action Hook: The script is hooked to the admin_footer action, ensuring its execution when the admin interface is being rendered.

3. Detect Block Editor: It first checks if the current screen involves the Block Editor by utilizing the get_current_screen function.

4. Inline JavaScript Initialization: When the Block Editor is confirmed, the script injects an inline JavaScript section into the admin footer.

5. Timeout-based Execution: Within the inline script, a setTimeout function is employed. This delay mechanism allows users a brief moment to finish their interactions before the panel expansion takes place.

6. Mutation Observer: The script employs the MutationObserver API to watch for changes within the Block Editor’s designated sidebar area.

7. Detection and Action: When a mutation of type 'childList' is detected, specifically involving elements with the class block-editor-block-inspector, the observer triggers a series of actions.

8. Clear Previous Timeout: If there was an existing delay timer (via activeTimer), it is cleared to reset the countdown.

9. Setting Up Observer: The observer is established, targeting a persistent parent container (div.interface-navigable-region.interface-interface-skeleton__sidebar) within the sidebar.

10. Delayed Action: The observer’s callback initiates a setTimeout to delay the expansion. This delay of 500 milliseconds allows users to complete their interactions before the expansion occurs.

11. Panel Expansion: Upon delay completion, the expandPanels function is invoked. This function finds and expands all collapsed panels in the sidebar by simulating button clicks.

12. Persistent Functionality: By observing a higher-level, persistent container, the script maintains its functionality even when individual panels are refreshed or re-rendered, as is the case when the sidebar is opened and closed.