"_lowairspeed" variable in Mission Planner HUD.cs

While working on the plugin feature and looking through the mission planner source code, I noticed that there is _lowairspeed property defined in HUD.cs :

[System.ComponentModel.Browsable(true), System.ComponentModel.Category("Values")]
public bool lowairspeed
{
    get { return _lowairspeed; }
    set
    {
        if (_lowairspeed != value)
        {
            _lowairspeed = value;
            this.Invalidate();
        }
    }
}

when this variable is set to true, the airspeed text is drawn in red on the HUD.

However, I couldn’t find any configuration option in mission planner related to this code.

It seems that this code reserved for future use, but I would like to confirm that I’m understanding this correctly.