You're reading the documentation for an older, but still supported, version of ROS 2. For information on the latest version, please have a look at Humble.
Citations
If you use ROS 2 in your work please cite the 2022 Science Robotics paper Robot Operating System 2: Design, architecture, and uses in the wild.
Macenski, T. Foote, B. Gerkey, C. Lalancette, W. Woodall, “Robot Operating System 2: Design, architecture, and uses in the wild,” Science Robotics vol. 7, May 2022.
@article{
doi:10.1126/scirobotics.abm6074,
author = {Steven Macenski and Tully Foote and Brian Gerkey and Chris Lalancette and William Woodall },
title = {Robot Operating System 2: Design, architecture, and uses in the wild},
journal = {Science Robotics},
volume = {7},
number = {66},
pages = {eabm6074},
year = {2022},
doi = {10.1126/scirobotics.abm6074},
URL = {https://www.science.org/doi/abs/10.1126/scirobotics.abm6074}
}