Add `.warning` class for doc author use

This is designed to be compatible with rustdoc's version, in
https://github.com/rust-lang/rust/pull/106561

1 files changed, 26 insertions, 0 deletions

diff --git a/guide/src/format/mdbook.md b/guide/src/format/mdbook.md
index 2872b250..15b8d1a7 100644
--- a/guide/src/format/mdbook.md
+++ b/guide/src/format/mdbook.md
@@ -314,3 +314,29 @@ contents (sidebar) by including a `\{{#title ...}}` near the top of the page.
 ```hbs
 \{{#title My Title}}
 ```
+
+## HTML classes provided by mdBook
+
+The `class="warning"` can be applied to make a warning, or similar note, stand out.
+
+```html
+<div class="warning">
+
+This is a bad thing that you should pay attention to.
+
+Warning blocks should be used sparingly in documentation, to avoid "warning
+fatique," where people are trained to ignore them because they usually don't
+matter for what they're doing.
+
+</div>
+```
+
+<div class="warning">
+
+This is a bad thing that you should pay attention to.
+
+Warning blocks should be used sparingly in documentation, to avoid "warning
+fatique," where people are trained to ignore them because they usually don't
+matter for what they're doing.
+
+</div>