How to use the roosterjs-editor-plugins.Watermark function in roosterjs-editor-plugins

private initEditor() {
        let pluginList = this.state.pluginList;
        editorInstanceToggleablePlugins = {
            hyperlink: pluginList.hyperlink ? new HyperLink(this.getLinkCallback()) : null,
            paste: pluginList.paste ? new Paste() : null,
            contentEdit: pluginList.contentEdit
                ? new ContentEdit(this.getContentEditOptions())
                : null,
            watermark: pluginList.watermark ? new Watermark(this.state.watermarkText) : null,
            imageResize: pluginList.imageResize ? new ImageResize() : null,
            tableResize: pluginList.tableResize ? new TableResize() : null,
            pickerPlugin: pluginList.pickerPlugin
                ? new PickerPlugin(new SampleColorPickerPluginDataProvider(), {
                      elementIdPrefix: 'samplepicker-',
                      changeSource: 'SAMPLE_COLOR_PICKER',
                      triggerCharacter: ':',
                      isHorizontal: true,
                  })
                : null,
            customReplace: pluginList.customReplace ? new CustomReplacePlugin() : null,
        };
        let plugins = [
            ...Object.keys(editorInstanceToggleablePlugins).map(
                k => (editorInstanceToggleablePlugins as any)[k]
            ),

features.defaultShortcut = (document.getElementById('defaultShortcutCheckbox') as HTMLInputElement).checked;
        features.smartOrderedList = (document.getElementById('smartOrderedListCheckbox') as HTMLInputElement).checked;
        plugins.push(new ContentEdit(features));

        let defaultFeatures = getDefaultContentEditFeatures();
        let keys = Object.keys(defaultFeatures);
        for (let key of keys) {
            if (key != 'smartOrderedListStyles' && features[key] != defaultFeatures[key]) {
                featuresChanged = true;
                break;
            }
        }
    }

    if ((document.getElementById('watermarkCheckbox') as HTMLInputElement).checked) {
        plugins.push(new Watermark('Type content here...'));
    }

    if ((document.getElementById('imageResizeCheckbox') as HTMLInputElement).checked) {
        plugins.push(new ImageResize());
    }

    if ((document.getElementById('tableResizeCheckbox') as HTMLInputElement).checked) {
        plugins.push(new TableResize());
    }

    plugins.push(new ShowCursorPosition(document.getElementById('cursorPosition')));
    plugins.push(new ShowFromState(document.getElementById('formatState')));

    let defaultFormat: DefaultFormat = {};

    if ((document.getElementById('boldCheckbox') as HTMLInputElement).checked) {