Change:
beta and nightly ignore the default-on configuration of "Auto-hide trait implementation documentation" On stable  looks like: ! While it looks like: ! And (as of 2021-05-17): ! Going to and toggling "Auto-hide trait implementation documentation" off makes stable look the same as beta, so it definitely seems like beta/nightly are just ignoring this toggle.
This is due to the refactoring we've been doing with the expand / collapse toggles, wrapping them in tags. The code that expands and collapses them based on settings is here: You can see there's an entry for handling "implementors" but not one for "implementations." Right now, both implementors and implementations get wrapped in a tag with . We need to update this Rust code: So that it generates for implementors and for implementations. And then update the JS to add a clause for implementations.
Assigning priority as discussed in the of the Prioritization Working Group. label -I-prioritize +P-medium
I'm having trouble figuring out what fields to check in to figure out if we're rendering an implementor or an implementation. If someone's able to point me in the right direction I'd appreciate it!
Well, I think I handled it in (funny that I was noticed it and fixed it on my side and someone else find it out too).

Discussion:
let open_details = |close_tags: &mut String| { if toggled { close_tags.insert_str(0, "</details>"); <del> "<details class="rustdoc-toggle implementors-toggle" open><summary>" </del> <ins> "<details class="rustdoc-toggle implementors-toggle"><summary>" </ins> } else { "" }

var hideMethodDocs = getSettingValue("auto-hide-method-docs") === "true"; var hideImplementors = getSettingValue("auto-collapse-implementors") !== "false"; <ins> var hideImplementations = getSettingValue("auto-hide-trait-implementations") !== "false"; </ins> var hideLargeItemContents = getSettingValue("auto-hide-large-items") !== "false"; <del> onEachLazy(document.getElementsByTagName("details"), function (e) { var showLargeItem = !hideLargeItemContents && hasClass(e, "type-contents-toggle"); var showImplementor = !hideImplementors && hasClass(e, "implementors-toggle"); if (showLargeItem || showImplementor) { </del> <ins> function openImplementors(id) { var list = document.getElementById(id); if (list !== null) { onEachLazy(list.getElementsByClassName("implementors-toggle"), function(e) { e.open = true; }); } } if (!hideImplementations) { openImplementors("trait-implementations-list"); openImplementors("blanket-implementations-list"); } if (!hideImplementors) { openImplementors("implementors-list"); } onEachLazy(document.getElementsByClassName("rustdoc-toggle"), function (e) { if (!hideLargeItemContents && hasClass(e, "type-contents-toggle")) { </ins> e.open = true; } if (hideMethodDocs && hasClass(e, "method-toggle")) {

} // @has manual_impl/struct.S3.html '//*[@class="trait"]' 'T' <del> // @has  - '//details[@open=""]/div[@class="docblock"]' 'Docs associated with the S3 trait implementation.' </del> <ins> // @has  - '//details/div[@class="docblock"]' 'Docs associated with the S3 trait implementation.' // @!has  - '//details[@open=""]/div[@class="docblock"]' 'Docs associated with the S3 trait implementation.' </ins> // @has  - '//details[@open=""]/div[@class="docblock"]' 'Docs associated with the S3 trait b_method implementation.' // @!has - '//div[@class="impl-items"]/details[@open=""]//div[@class="docblock"]' 'Docs associated with the trait a_method definition.' // @has - '//div[@class="impl-items"]/details//div[@class="docblock"]' 'Docs associated with the trait a_method definition.'