Include summary in list of inconsistent elements

README.md

@@ -94,7 +94,7 @@ All tabbable elements are focusable, but not all focusable elements are tabbable
 ## More details
 
 - **Tabbable tries to identify elements that are reliably tabbable across (not dead) browsers.** Browsers are stupidly inconsistent in their behavior, though — especially for edge-case elements like `<object>` and `<iframe>` — so this means *some* elements that you *can* tab to in *some* browsers will be left out of the results. (To learn more about that stupid inconsistency, see this [amazing table](https://allyjs.io/data-tables/focusable.html)). To provide better consistency across browsers and ensure the elements you *want* in your tabbables list show up there, **try adding `tabindex="0"` to edge-case elements that Tabbable ignores**.
-- (Exemplifying the above ^^:) **The tabbability of `<iframe>`s, `<embed>`s, `<object>`s, and `<svg>`s is [inconsistent across browsers](https://allyjs.io/data-tables/focusable.html)**, so if you need an accurate read on one of these elements you should try giving it a `tabindex`. (You'll also need to pay attention to the `focusable` attribute on SVGs in IE & Edge.) But you also might *not* be able to get an accurate read — so you should avoid relying on it.
+- (Exemplifying the above ^^:) **The tabbability of `<iframe>`s, `<embed>`s, `<object>`s, `<summary>`s, and `<svg>`s is [inconsistent across browsers](https://allyjs.io/data-tables/focusable.html)**, so if you need an accurate read on one of these elements you should try giving it a `tabindex`. (You'll also need to pay attention to the `focusable` attribute on SVGs in IE & Edge.) But you also might *not* be able to get an accurate read — so you should avoid relying on it.
 - **Radio groups have some edge cases, which you can avoid by always having a `checked` one in each group** (and that is what you should usually do anyway). If there is no `checked` radio in the radio group, *all* of the radios will be considered tabbable. (Some browsers do this, otherwise don't — there's not consistency.)
 - If you're thinking, "Why not just use the right `querySelectorAll`?", you *may* be on to something ... but, as with most "just" statements, you're probably not. For example, a simple `querySelectorAll` approach will not figure out whether an element is *hidden*, and therefore not actually tabbable. (That said, if you do think Tabbable can be simplified or otherwise improved, I'd love to hear your idea.)
 - jQuery UI's `:tabbable` selector ignores elements with height and width of `0`. I'm not sure why — because I've found that I can still tab to those elements. So I kept them in. Only elements hidden with `display: none` or `visibility: hidden` are left out.