Breathable air on the moon (sources, gas composition, humidity, filtration, purity, removal of CO2 and other waste products and pollutants, temperature).
Clicking on a [+] will expand the category to show sub-categories if any exist.
You can create a new category with this button. Leave the Category: in place.
<inputbox> type=create default=Category: buttonlabel=Create Category </inputbox>
You will still need to enter [[Category:Air Supply]] in your new category to have it show up in this list.