private static boolean isAlphanumeric(char c) {
        return (c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z');
    }
Check if a hostLabel is valid.

@param hostLabel Host label to check.
@param allowDots Set to true to allow dots as separators.
@return true if the label is valid.
smithy-rules-engine/src/main/java/software/amazon/smithy/rulesengine/language/syntax/expressions/functions/IsValidHostLabel.java