Global data affect all layers. The most trivial example is padstack: it has a hole and potentially a copper ring on all -layers. Another global object pcb_data_t holds is an element. A padstack +layers. A padstack directly under the board's pcb_data_t is considered a "via" (by convention, by purpose), a padstack under subcircuit's pcb_data_t is usually a "pin" or "pad" (when has a term ID) or a "via". The quoted terms don't exist @@ -119,7 +119,7 @@ in the code, they are just conventions. Padtsacks are vertical constructions, they may affect multiple layers.
-The third global object is subcircuit; using its own layer list, it potentially +The other global object is subcircuit; using its own layer list, it potentially can affect all layers of the board. The children objects of a subcircuit is a pcb_data_t, which allows arbitrary (loop-free) recursion in data.