What does export tag in package.xml do?

edit

What does the following block of code in a package.xml do?

<export>
  <gazebo_ros gazebo_model_path="${prefix}/models"/>
</export>

I thought if I have this code in my package's package.xml & catkin_make the package & source the corresponding setup.bash file, the GAZEBO_MODEL_PATH env variable will be set automatically instead of having to set it manually. But that doesn't look like the case.

Can anyone please explain this? Thanks!

P.S: I was trying to follow this tutorial

P.P.S: I'm using ROS Noetic. & Gazebo-11