void expectChar(char expected) {
            if (!valid()) {
                throw new IllegalInputException("Expected '" + expected + "', end of spec reached at " + spec());
            }
            var act = peek();
            if (act != expected) {
                throw new IllegalInputException("Expected '" + expected + "', got '" + act + "' at " + spec());
            }
            step();
        }
Decide if sortorder is ascending or not.
container-search/src/main/java/com/yahoo/search/query/Sorting.java