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This is related to theme feature toggles provided by Drupal core. Themes and plug-ins can define sets of features adding to the pool of available features.
They must be set from the theme .info or plug-in .pinfo file.
The FEATURE_KEY is the machine readable name and FEATURE_NAME is the human readable name used in the theme settings form. All feature keys must be unique and they cannot be overridden.
If the features are set within a plug-in, enabling it through the theme settings form will enable the plug-in. If none of the features are enabled for a plug-in, none of the code associated with the plug-in will ever load. This can keep code associated with the feature very focused on its purpose.