Emit valid HTML from rustdoc

Previously, tidy-html5 (`tidy`) would complain about a few things in our
HTML. The main thing is that `<summary>` tags can't contain `<div>`s.
That's easily fixed by changing out the `<div>`s for `<span>`s with
`display: block`.

However, there's also a rule that `<span>`s can't contain heading
elements. `<span>` permits only "phrasing content"
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/span, and
`<h3>` (and friends) are "Flow content, heading content, palpable
content".
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/Heading_Elements

We have a wrapping `<div>` that goes around each `<h3>`/`<h4>`,
etc. We turn that into a `<section>` rather than a `<span>` because
`<section>` permits "flow content".
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/section

After this change we get only three warnings from tidy, run on
struct.String.html:

line 6 column 10790 - Warning: trimming empty <span>
line 1 column 1118 - Warning: <link> proprietary attribute "disabled"
line 1 column 1193 - Warning: <link> proprietary attribute "disabled"

The empty `<span>` is a known issue - there's a span in front of the
search box to work around a strange Safari issue.

The `<link>` attributes are the non-default stylesheets. We can probably
refactor theme application to avoid using this proprietary "disabled"
attribute.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/test/rustdoc/const-generics/add-impl.rs b/src/test/rustdoc/const-generics/add-impl.rs
index 7e38eb8369a..e54f9a57ae4 100644
--- a/src/test/rustdoc/const-generics/add-impl.rs
+++ b/src/test/rustdoc/const-generics/add-impl.rs
@@ -7,7 +7,7 @@ pub struct Simd<T, const WIDTH: usize> {
     inner: T,
 }
 
-// @has foo/struct.Simd.html '//div[@id="trait-implementations-list"]//div/h3[@class="code-header in-band"]' 'impl Add<Simd<u8, 16_usize>> for Simd<u8, 16>'
+// @has foo/struct.Simd.html '//div[@id="trait-implementations-list"]//h3[@class="code-header in-band"]' 'impl Add<Simd<u8, 16_usize>> for Simd<u8, 16>'
 impl Add for Simd<u8, 16> {
     type Output = Self;