Location

Maximum Damage
[...]
//sets grass Hardness to 256
pick.maxDamage = 256;

Is it just the "sets grass hardness" part?

Yes.
Although there was also 404 with the "view/edit on github" link in the pop-up bar at the bottom.

not sure about that 404, but typo is fixed, heads up, this is the docs repo
https://github.com/jaredlll08/CraftTweaker-Documentation