Many sites have an electronic logbook, i.e. an online system that keeps entries with texts or images. CSS itself does not include an electronic logbook, but it can be linked to an existing site-specific system.
If a logbook is available at your site, several CSS tools will allow users to send text or screenshots to it. The Data Browser and BOY for example allow sending a screenshot to the logbook, while the alarm system tools can send a description of currently active alarms to the logbook. This can be done directly from for example the context menu of a BOY display, without need to start an external tool to create a screenshot, saving it to a file, then logging into the logbook to download the saved file etc.
This plugin defines the API for making logbook entries as well as an extension point for the actual implementation.
Code that allows logbook entry generation depends on this plugin and can query it for the presence of an implementation. If no implementation of the logbook extension point is available, the logbook functionality should simply be disabled, for example by hiding corresponding menu entries.
Site-specific plugins provide the implementation for creating a logbook entry. There must be at most one such implementation. With no implementation available, the logbook functionality is simply disabled. When multiple implementations are available, the logbook support will report an error.