et after = (line, col, span) => {
            if (line > span[2]) { return true; }
            if (line == span[2]) { return col > span[3]; }
            return false;
        };

        let intersects = (span, from, to) => {
            if (!before(to.line + 1, to.ch + 1, span) &&
                !after(from.line + 1, from.ch + 1, span)) {
                return true;
            }
            return false;
        };

        let el_file_tree = document.getElementById("file_tree");
        let el_test_tr