Write docs for the multipleItemsY feature

docs/.vuepress/config.js

@@ -15,6 +15,7 @@ module.exports = {
           "/examples/Disabled.md",
           "/examples/DisabledItems.md",
           "/examples/Responsive.md",
+          "/examples/MultipleItemsY.md",
         ],
       },
     ],

docs/examples/MultipleItemsY.md

+# Example 9: Multiple Items per field
+
+Grid with multiple items per slot (overlaps only in y direction possible,
+width of every item has to be `1`). The items are placed in the grid automatically.
+
+To allow this behaviour, the grid component has to receive the prop `multiple-items-y` with the value `true`.
+
+<ClientOnly>
+<script setup>
+import Example9MultipleItemsY from "../../example/src/Example9MultipleItemsY.vue";
+</script>
+
+<Example9MultipleItemsY />
+</ClientOnly>

docs/guide/index.md

@@ -244,3 +244,17 @@ Examples for such a mechanism can be found in Examples 4 and 5.
 :::
 
 To handle movements from one grid to another, the attributes `gridId` and `originGridId` of the event will help.
+
+## Overlapping grid items
+
+If two items overlap, the one which is defined later in the array will be on top of the other one.
+They cannot be dragged.
+
+If you want to have overlapping items which can be dragged, there exists the `multipleItemsY` prop.
+If this is set to `true`, items can be dragged on top of each other. The items will be stacked horizontally.
+This is useful for e.g. a calendar-like frontend.
+
+::: danger
+If `multipleItemsY` is set to `true`, the `w` property of all items has to be set to `1`.
+Otherwise, this will lead to unexpected behaviour.
+:::