The ID of the GSettings schema used by this applet
This only takes effect when you've also set settings_prefix, and is used by the panel managemen to both initialise and delete your per-instance settings, respectively.
As an example, the Budgie Menu Applet uses the schema:
`com.solus-project.budgie-menu`
as defined by the accompanying gschema XML file. Providing an incorrect schema ID is considered programmer error.