"While scientists study how nature works, engineers create new things, such as products, websites, environments, and experiences. Because engineers and scientists have different objectives..."
Here are some examples of using Drupal's states API. It shows the use of OR and XOR (which only work with jQuery 1.8 or above, apparently). More examples can be found in the examples project in the form example module.
Here's a Tampermonkey script which adds a Save and Edit button to the mini panels content edit page for every site :) If you don't have the button, then every time you save, you are brought back to the mini-panels content overview page, which gets kind of long.
Here's an example of how to theme a book navigation menu. This example creates a theme function that can be used to output the book outline in any place. There is an example in this module that create a panels pane.