Is there a guide or spec to how Vim defines text/a word?

I'm thinking of cursor motions like 'e' or 'w'. If you paste in a URL put your cursor on the starting 'h' and press 'e', your cursor will move to the : in the URL.

That's different from how operating systems navigate text on ctrl-right so I'm wondering if Vim modes/clones have a spec or definition, or if they copy through observation.