Broken SharePoint 2013 webpart page

If you've been editing custom pages using SharePoint Designer, you know how fragile they can be. 

A wrong key can break a page that worked a few minutes ago and you get the generic error:

 "Unable to display this Web Part. To troubleshoot the problem, open this Web page in a Microsoft SharePoint Foundation-compatible HTML editor such as Microsoft SharePoint Designer. If the problem persists, contact your Web server administrator."

Solutions:

1. Routinely create backup copies of the page for comparison and restoration
2. SharePoint Designer likes to randomly add   characters to your markup which will break the page.  Search for and delete these.
3. Never delete the original new form from a page.  Hide it, but never delete it.  This will keep the attachment functionality working correctly.