add #overrideLevel method to concrete numberings

ts/numbering/num.ts

@@ -1,4 +1,5 @@
 import { Attributes, XmlAttributeComponent, XmlComponent } from "../docx/xml-components";
+import { LevelForOverride } from "./level";
 
 class AbstractNumId extends XmlComponent {
 
@@ -29,4 +30,51 @@ export class Num extends XmlComponent {
         this.root.push(new AbstractNumId(abstractNumId));
         this.id = numId;
     }
+
+    public overrideLevel(num: number, start?: number): LevelOverride {
+        const olvl = new LevelOverride(num, start);
+        this.root.push(olvl);
+        return olvl;
+    }
+}
+
+class LevelOverrideAttributes extends XmlAttributeComponent<{ilvl: number}> {
+    protected xmlKeys = {ilvl: "w:ilvl"};
+}
+
+class LevelOverride extends XmlComponent {
+    private levelNum: number;
+    private lvl?: LevelForOverride;
+
+    constructor(levelNum: number, start?: number) {
+        super("w:lvlOverride");
+        this.root.push(new LevelOverrideAttributes({ilvl: levelNum}));
+        if (start !== undefined) {
+            this.root.push(new StartOverride(start));
+        }
+        this.levelNum = levelNum;
+    }
+
+    get level(): LevelForOverride {
+        let lvl: LevelForOverride;
+        if (!this.lvl) {
+            lvl = new LevelForOverride(this.levelNum);
+            this.root.push(lvl);
+            this.lvl = lvl;
+        } else {
+            lvl = this.lvl;
+        }
+        return lvl;
+    }
+}
+
+class StartOverrideAttributes extends XmlAttributeComponent<{val: number}> {
+    protected xmlKeys = {val: "w:val"};
+}
+
+class StartOverride extends XmlComponent {
+    constructor(start: number) {
+        super("w:startOverride");
+        this.root.push(new StartOverrideAttributes({val: start}));
+    }
 }