zindex fixes to SplitButton

src/components/splitbutton/SplitButton.vue

@@ -23,11 +23,34 @@ import DomHandler from '../utils/DomHandler';
 
 export default {
     props: {
-        label: String,
-        icon: String,
-		model: Array,
-        disabled: Boolean,
-        tabindex: String
+        label: {
+            type: String,
+            default: null
+        },
+        icon: {
+            type: String,
+            default: null
+        },
+		model: {
+            type: Array,
+            default: null
+        },
+        disabled: {
+            type: Boolean,
+            default: false
+        },
+        tabindex: {
+            type: String,
+            default: null
+        },
+        autoZIndex: {
+            type: Boolean,
+            default: true
+        },
+        baseZIndex: {
+            type: Number,
+            default: 0
+        },
     },
     data() {
         return {
@@ -53,6 +76,9 @@ export default {
             event.preventDefault();
         },
         onOverlayEnter() {
+            if (this.autoZIndex) {
+                this.$refs.overlay.style.zIndex = String(this.baseZIndex + DomHandler.generateZIndex());
+            }
             this.alignOverlay();
             this.bindOutsideClickListener();
         },

src/views/splitbutton/SplitButtonDoc.vue

@@ -109,10 +109,22 @@ export default {
                                 <td>When present, it specifies that the component should be disabled.</td>
                             </tr>
                             <tr>
-							<td>tabIndex</td>
+                                <td>tabindex</td>
                                 <td>string</td>
                                 <td>null</td>
                                 <td>Index of the element in tabbing order.</td>
+                            </tr>
+                            <tr>
+                                <td>autoZIndex</td>
+                                <td>boolean</td>
+                                <td>true</td>
+                                <td>Whether to automatically manage layering.</td>
+                            </tr>
+                            <tr>
+                                <td>baseZIndex</td>
+                                <td>number</td>
+                                <td>0</td>
+                                <td>Base zIndex value to use in layering.</td>
                             </tr>
 						</tbody>
 					</table>