This Quill editor has been setup with two ArcsJs plugins: local font picker and a local photo picker.
To try the font picker, select the text you want to update. Then click on the drop-down menu in the top left corner. This will load the local fonts from your computer. When you pick a font, the plugin will send only the selected font to the base application. Because the font picker is executed in a secure environment, only the selected font is viewable to external parties. This plugin highlights how developers can create customized UI while restricting access to the user's data. In the list of fonts, the developer has chosen to highlight some that might be of interest to the user.
To use the photo picker, click the photo icon near the right side of the toolbar. The first time you load the plugin, your browser will ask you to select a folder with photos from your local machine. Once you do this, the chosen photos will load into the ArcsJs powered photo picker.
For more information on these plugins, checkout the code here.