What is the functionality of datapoints having underline "_" as first character

The use of underline "_" as first character is reserved for internal datapoint types and internal datapoint names of WinCC OA.
Internal datapoints are an essential part of WinCC OA. In internal datapoints basic information of the systemstate and configuration setting are stored. By sending internal datapoints basic system actions are triggered.
the underline "_" may also be used as first character to define project-specific internal datapoint types and internal datapoint names. In these project specific internal datapoints, specific project setting and information may be saved.
By default the tree view in the PARA-module is opened without displaying the internal datapoints. Clicking on the "Internal datapoints" check box enables to display the internal datapoints of WinCC OA.