Warn if multipleItemsY is true and some items have width > 1

src/DragGrid.vue

@@ -311,6 +311,13 @@ export default {
     items() {
       if (!this.multipleItemsY) return this.value;
 
+      if (this.value.some((item) => item.w > 1)) {
+        console.warn(
+          "You are using multipleItemsY but some items have a width greater than 1.",
+          "This is not supported and will lead to unexpected behaviour."
+        );
+      }
+
       // calculate numSiblings for each field
       // First dimension: the columns
       let xSiblings = [];