Shadow template is a tool to preview alternate templates or markup without editing the page each time. The link for it shows up in custom tools toolbar of every page. The script also allows to try out different parameters for the same template without editing the page and going through the whole, edit, preview, and save process. This is inspired by, and quite similar in functionality to Template sandbox.
Either choose a template, e.g. "templateBazooka from the drop down or enter a template name in the first input box.
Enter the name of the alternate template to replace e.g. "templateGrenade"
The script also allows adding arbitrary markup to the page, once the checkbox is clicked. This can be a template call, e.g.:
Note: In this example, pay close attention to the placement of commas and other punctuation. For people who aren't familiar with programming (and even those who are!), a common mistake when writing code is to accidentally delete, forget, or misplace critical symbols like commas or quotation marks. This can cause a syntax error that breaks the code. Carefully follow the convention shown here when using importArticles.