Add examples of forms in dropdown menus

docs/4.0/components/dropdowns.md

@@ -474,6 +474,55 @@ Separate groups of related menu items with a divider.
 </div>
 {% endexample %}
 
+## Menu forms
+
+Put a form within a dropdown menu, or make it into a dropdown menu, and use [margin or padding utilities]({{ site.baseurl }}/docs/{{ site.docs_version }}/utilities/spacing/) to give it the negative space you require.
+
+{% example html %}
+<div class="dropdown-menu">
+  <form class="px-4 py-3">
+    <div class="form-group">
+      <label for="exampleDropdownFormEmail1">Email address</label>
+      <input type="email" class="form-control" id="exampleDropdownFormEmail1" placeholder="email@example.com">
+    </div>
+    <div class="form-group">
+      <label for="exampleDropdownFormPassword1">Password</label>
+      <input type="password" class="form-control" id="exampleDropdownFormPassword1" placeholder="Password">
+    </div>
+    <div class="form-check">
+      <label class="form-check-label">
+        <input type="checkbox" class="form-check-input">
+        Remember me
+      </label>
+    </div>
+    <button type="submit" class="btn btn-primary">Sign in</button>
+  </form>
+  <div class="dropdown-divider"></div>
+  <a class="dropdown-item" href="#">New around here? Sign up</a>
+  <a class="dropdown-item" href="#">Forgot password?</a>
+</div>
+{% endexample %}
+
+{% example html %}
+<form class="dropdown-menu p-4">
+  <div class="form-group">
+    <label for="exampleDropdownFormEmail2">Email address</label>
+    <input type="email" class="form-control" id="exampleDropdownFormEmail2" placeholder="email@example.com">
+  </div>
+  <div class="form-group">
+    <label for="exampleDropdownFormEmail2">Password</label>
+    <input type="password" class="form-control" id="exampleDropdownFormEmail2" placeholder="Password">
+  </div>
+  <div class="form-check">
+    <label class="form-check-label">
+      <input type="checkbox" class="form-check-input">
+      Remember me
+    </label>
+  </div>
+  <button type="submit" class="btn btn-primary">Sign in</button>
+</form>
+{% endexample %}
+
 ## Disabled menu items
 
 Add `.disabled` to items in the dropdown to **style them as disabled**.