function determineSubPixelRoundingRule(subPixelRoundingRules) {
    if (typeof subPixelRoundingRules === 'number') {
        return normalizeSubPixelRoundingRule(subPixelRoundingRules);
    }

    if (!subPixelRoundingRules || !$.Browser) {
        return DEFAULT_SUBPIXEL_ROUNDING_RULE;
    }

    var subPixelRoundingRule = subPixelRoundingRules[$.Browser.vendor];

    if (isSubPixelRoundingRuleUnknown(subPixelRoundingRule)) {
        subPixelRoundingRule = subPixelRoundingRules['*'];
    }

    return normalizeSubPixelRoundingRule(subPixelRoundingRule);
}
Ensures the returned value is always a valid subpixel rounding enum value,
defaulting to 'NEVER' if input is missing or invalid.
@private

@param {Object} subPixelRoundingRules - A subpixel rounding enum values dictionary [{@link BROWSERS}] --> {@link SUBPIXEL_ROUNDING_OCCURRENCES}.
@returns {SUBPIXEL_ROUNDING_OCCURRENCES} Returns the determined subpixel rounding enum value for the
current browser.