Tip: You can pass through extra data with your sites coords, that is then in cells sites output.

[hayden-t]

var sites = [ {x: 200, y: 200, specialValue: yes}]

and then that specialValueis now attached in the output of cells when the voronoi is calculated:

diagram.cells[i].site['specialValue']

[Wuzzy2]

This is a bad idea to do it like this because you never know when the API changes and touches your custom value.

JavaScript offers symbols for that use case. https://javascript.info/symbol

Anyway, I think the documentation should mention that the cells sites contain references to your original sites objects, since this is useful to know. Otherwise, you might assumes the cells sites are just copies of those sites.