i am not aware of any parser that does that differently, but i would also argue that this is not the job of parsers. after parsing (or before exporting) there should be a data validation step based on whitelists.

so the user can send in unknown fields all they want, the code will only accept the username and firstname strings, and ignore the other ones.

same with fetching data and sending it to the user. i fetch only the fields i want and create the correct datastructures before invoking the marshaling step.

there are no footguns. if you expect your parser to protect you you are using it wrong. they were not designed for that.

input -> parse -> extract the fields we want, which are valid -> create a data-structure with those fields.

data -> get fields i want -> create datastructures with only wanted fields -> write to output format