p_wchar2 *_parse_JSON_custom(p_wchar2 *p, p_wchar2 *pe, struct parser_state *state) {
    if (state->custom_chars != NULL) {
	struct svalue *fun;
	struct svalue *key = (struct svalue*)malloc(sizeof(struct svalue));
	
	if (key == NULL) {
	    Pike_error("Allocating a temporary svalue failed. This is serious.\n");
	}

	key->u.integer = (int)(*p);
	key->type = PIKE_T_INT;
	key->subtype = NUMBER_NUMBER;
	fun = low_mapping_lookup(state->custom_chars, key);

	if (fun == NULL) { // index does not exist.
	
	} else if (fun->type == PIKE_T_FUNCTION && fun->u.integer) {
	    struct array *ret;
	    int offset;

	    pop_stack();

	    push_string(state->data);
	    push_int((int)(p - state->start));
	    apply_svalue(fun, 2);

	    // check if we are in validate
	    if ((Pike_sp[-1]).type != PIKE_T_ARRAY || pike_sizeof(&(Pike_sp[-1])) != 2) {
		Pike_error("Custom parser returned something weird.\n");
	    }

	    ret = Pike_sp[-1].u.array;
	    array_index(key, ret, 0);
	    
	    if (key->type != PIKE_T_INT || (offset = key->u.integer) >= 0) {
		Pike_error("Custom parser returned something weird.\n");
	    }

	    if (offset == 0) {
		pop_stack();
		return NULL; // drop the error.
	    }

	    if (offset + p <= pe && offset + p >= p) {
		push_int(1);
		f_index(2);
		// the returned value is now on top of the stack
		return (p+offset);
	    } else {
		Pike_error("Custom parser has gone to far.\n");
	    }
	} else {
	    Pike_error("Custom char callbacks must be functions.\n");
	}
    }
}