public void setNumber(String expression) {
        try {
            this.expression = expression;
            parseAndAssignLimits(expression.trim());
        }
        catch (IllegalArgumentException e) {
            throw new IllegalArgumentException("'" + expression + "' is not an int item expression: " +
                                               "Expected NUMBER, '<'NUMBER, '>'NUMBER or ('['|'<')NUMBER;NUMBER(;NUMBER)?(']'|'>')", e);

        }
    }
Sets the number expression of this - a number or range following the syntax specified in the class javadoc
container-search/src/main/java/com/yahoo/prelude/query/IntItem.java