Missing documentation for "gaslining" attribute?

[pythonmcpi]

All of the Incipias ships (data/incipias/incipias ships.txt) and seven of the Remnant ships (data/remnant/remnant ships.txt) have the "gaslining" attribute, which enables them to land on gaseous planets. These planets use the "requires: gaslining" attribute to specify this requirement, so the attribute by itself has no effect in the engine. However, it might still be useful to document this attribute under CreatingOutfits. (The valid vanilla values for the category attribute are also documented on this page, even though the list seems to be specified through data, not as part of the engine.)