If you have developed a dashboard addon and you'd like to serve a demo site, you'll need to protect your dashboard.
When clicking on "Add link" in the "Social Links" Dashboard page there is a dropdown with possible social link entries like Facebook, Twitter, Instagram and so on. Here I'll show how to add other links with the example of StackExchange.
This How-To is for adding fonts to the Redactor plugin "fontfamily" in a package. The original fontfamily plugin just adds a dropdown with a few fonts.
Change the default " :: " separator to something else.
In 5.6, we could use $_SESSION but in 5.7, there is a built-in session class from Symphony.
Change the default photo of the day login page background image to a custom background image of your choice.
Change the default values for the block and block area custom style sliders.
Use Composer to declare your dependencies and download a third party library for use in your package. This example will use Stripe PHP.