That linked document must be written for a very specific target audience because it seems to use a lot of words without providing context of the problem it's solving. The example in their GH repo is a little more "this does what?": https://github.com/jina-ai/docarray#example-1-represent-mult... although even that is a little "don't worry where there seemingly random methods on Document came from" which https://docarray.jina.ai/api/docarray.document/#docarray.doc... seems to fill in a little more
Then again, I guess folks were similarly confused in the past: