Set the value of attribute @racket[_key] to @racket[_value] in @racket[_txexpr]. Return the updated @racket[_txexpr]. Duplicate attributes, if they exist, are resolved using @racket[attr->hash]. @racket[attr-set] only accepts one key and one value; @racket[attr-set*] accepts any number.
Set the value of attribute @racket[_key] to @racket[_value] in @racket[_txexpr]. Return the updated @racket[_txexpr]. Duplicate attributes, if they exist, are resolved using @racket[attrs->hash]. @racket[attr-set] only accepts one key and one value; @racket[attr-set*] accepts any number.