SoBlinker(3) on Linux
The text d2a720f82d55, as Debian 8 (Jessie) shipped it.
The SoBlinker class is a cycling switch node. This switch node cycles its children SoBlinker::speed number of times per second. If the node has only one child, it will be cycled on and off. Cycling can be turned off using the SoBlinker::on field, and the node then behaves like a normal SoSwitch node.