Confusing wording for is_ground_content

Chapter 3:

The is_ground_content attribute allows caves to be generated over the stone. This is essential for any node which may be placed during map generation underground. Caves are cut out of the world after all the other nodes in an area have generated.

This is confusingly worded. To be generated over the stone? What stone? I thought this is an Alien Diamond. And what does over mean? There are rhetorical questions.

What this attribute actually does is allow the cave generator to destroy this node when it is generated in the world

Also, this section failed to mention that true is the default here. This is tricky because often ppl forget it. As my personal rule of thumb: Everything that is part of the "natural world" (dirt, ores, etc.) should have true while "artificial" things like wooden planks, chests, furniture have it set to false. Many games forget to set this to false for nodes where it should be false.

I think is_ground_content is such a tricky variable that it might even get its own dedicated section.