Placing this control on a Publishing page triggers saving the publishing page when that page is in Edit mode and the user attempts to navigate to another page.
Assembly: Microsoft.SharePoint.Publishing (in Microsoft.SharePoint.Publishing.dll)
This control prevents data loss on publishing pages. When a page is in edit mode, and a user navigates to another page without executing __doPostback, this control automates the save process before the page is exited (using Internet Explorer's onBeforeUnload event). This can occur when a user clicks a link or closes the browser. This control is included by default on Publishing pages.