Theoretically, the footer and group row can have their own handlers, but as far as I can tell, those get mashed by the main column formatter. I wound up having to write something like the below. Am I missing something? Is there an easier way?

    /**
     * Format the column.
     * Uses this.callCounter to count the number of times
     * the method is called, which is then used by getFormatterMode
     */
    function formatMyColumn(cellvalue, options, rowObject) {
        var result = cellvalue;
        if (typeof this.callCounter == 'undefined') {
            this.callCounter = 1;
        } else {
            this.callCounter++;
        }
        var mode = getFormatterMode(this.callCounter, cellvalue, options, rowObject);
        switch (mode) {
            case modes.SUMMARY :
                // format for summary
            break;
            case modes.GROUPING:
                // format for group row
            break;
            case modes.FORMATTING:
                // format for regular row
            break;
        }
        return result;
    }
    
    /**
     * constants for the different modes that column formatters can be called in
     */
    var modes = {
        SUMMARY : 'SUMMARY',
        GROUPING : 'GROUPING',
        FORMATTING : 'FORMATTING'
    }
    
    /**
     * figure out what formatting mode we're in 
     * @todo    There's probably a better method than I'm 
     *          using based on the values and types of the 
     *          second-fourth parameters.
     *          In fact, options.rowId alone might be enough. 
     *          Need to do some more research.
     * @param {int}    counter      the number of times the formatter 
     *                                 function has been called for a given column
     * @param {Object} cellvalue    cellvalue from the formatter call
     * @param {Object} options      options from the formatter call
     * @param {Object} rowObject    rowObject from the formatter call
     */
    var getFormatterMode = function(counter, cellvalue, options, rowObject) {
        var result;
        if (counter !== options.rowId) {
            if (typeof options.rowId == 'string') {
                if (options.rowId === '') {
                    result = modes.SUMMARY;
                } else {
                    result = result = modes.GROUPING;
                }
            } else {
                result = modes.FORMATTING;
            }
        return result;
    };