Fixes #18768: Add migration docs for dropdowns

diff --git a/docs/migration.md b/docs/migration.md
index 0ef91b4be9e2e36d0d6da4071cfd11ae7632a9ff..88987d81dd9c24e8ede6f2357a70dd5c8795977b 100644 (file)
--- a/docs/migration.md
+++ b/docs/migration.md
@@ -104,6 +104,14 @@ New to Bootstrap 4 is the Reboot, a new stylesheet that builds on Normalize with
 
 - Dropped the `.btn-group-xs` class entirely given removal of `.btn-xs`.
 
+### Dropdowns
+
+- Switched from parent selectors to singular classes for all components, modifiers, etc.
+- Dropdowns can be built with `<div>`s or `<ul>`s now.
+- Rebuilt dropdown styles and markup to provide easy, built-in support for `<a>` and `<button>` based dropdown items.
+- Dropdown items now require `.dropdown-item`.
+- Dropdown toggles no longer require an explicit `<span class="caret"></span>`; this is now provided automatically via CSS's `::after` on `.dropdown-toggle`.
+
 ### Grid system
 
 - Added a new `~480px` grid breakpoint, meaning there are now five total tiers.