can you give me the history behind https://html.spec.whatwg.org/#spin-the-event-loop?

✦ The history of the "spin the event loop" algorithm is a journey from an informal "blocking" requirement to a rigorous, formalized "specification macro."

1. The Origin: Parser/Script Synchronization (October 2009)
   The algorithm was introduced by Ian Hickson on October 11, 2009, in commit 35847fe79f33b502a0e9271c9ee523e49e2e93da (https://github.com/whatwg/html/commit/35847fe79f33b502a0e9271c9ee523e49e2e93da) (SVN revision 4103).

• The Problem: The HTML5 specification needed a way to explain how the parser should stop executing a <script> while waiting for CSS (specifically @import) to finish loading, without "locking up" the entire browser.
• The Initial Solution: Hickson defined "spin the event loop" as a series of steps: stop the current task, allow the event loop to run, wait for a condition, and then queue a new task to resume the original algorithm. This
  effectively turned a synchronous script execution into an asynchronous "pause and resume" operation.

2. The Formalization: The "Spec Macro" (May 2019)
   For nearly a decade, the algorithm remained somewhat hand-wavy in its execution. It was significantly "rigorized" and refactored in May 2019 by Anne van Kesteren and Domenic Denicola in commit
   38c50c4ea111bd8f3ff60d2a49110a62a293c7ac (https://github.com/whatwg/html/commit/38c50c4ea111bd8f3ff60d2a49110a62a293c7ac).

• The Change: This commit added the formal definition of the algorithm as a "macro." It clarified that unlike a standard function call, "spin the event loop" expands into a series of steps that save the state (the execution
  context stack), run microtasks, and then "re-queue" the rest of the algorithm's steps as a new task.
• The Rationale: This cleanup was part of a larger effort to define "tasks" and "task queuing" as proper data structures in the spec, ensuring that browsers had a interoperable model for how asynchronous resumption should work.

3. Current Role
   Today, "spin the event loop" is the standard tool for spec authors whenever they need an algorithm to wait for something in a way that appears synchronous to the calling logic but must be asynchronous to the browser (like waiting
   for a stylesheet to load before running a script). It remains one of the most complex and critical "meta-algorithms" in the HTML specification.

annevk: ping https://github.com/WebKit/standards-positions/issues/586

I think the spec PR is ready to land