Related to: Sphinx Header Processing Example.
Here is the Excalidraw drawing demonstrating the creation of the filler, the header, and the subsequent header processing.
The original diagram is an Obsidian Excalidraw drawing. To view it, open this vault in Obsidian with the Excalidraw plugin installed and enabled.
The web version of the diagram is available here: https://link.excalidraw.com/readonly/6y7DRQlUhkkBMZScEONS.