NameSpacedKeys

Explanation on NameSpacedKeys

An item's complete NBT data obtained from Paper's /paper dumpitem command

From the image above, the NBT data that this command alters is located in the custom_data section, highlighted in pink. It's all of this:

custom_data={PublicBukkitValues: {"executableitems:ei-id": "test", "score:usage": 1}}

There are two NameSpacedKeys in here, one being "executableitems:ei-id": "test" and the other being "score:usage": Focusing on the first one, executableitems is the Namespace, ei-id is the Key, and test is the Content of the NameSpacedKey.

Similarly, for the second one, score is the Namespace, usage is the Key, and 1 is the Content.