px4 firmware iris_base xacro namespace property

edit

In the px4 firmware iris_base.xacro file: https://github.com/PX4/sitl_gazebo/bl...

there is a property "namespace" that is assigned multiple times to the namespace parameter in various macros. For example in the wind_plugin_macro:

<xacro:wind_plugin_macro
    namespace="${namespace}"
    wind_direction="0 0 1"
    wind_force_mean="0.7"
    xyz_offset="1 0 0"
    wind_gust_direction="0 0 0"
    wind_gust_duration="0"
    wind_gust_start="0"
    wind_gust_force_mean="0"
    />

where is this "namespace" intialised or passed from and how?