private static boolean tryEncoding(byte[] sig, byte b1, byte b2, byte b3,
            byte b4) {
        return ((sig[0] == b1) && (sig[1] == b2) && (sig[2] == b3) && (sig[3] == b4));
    }
Check for a four-byte signature.
<p>
Utility routine for detectEncoding ().
<p>
Always looks for some part of "<?XML" in a specific encoding.

@param sig
           The first four bytes read.
@param b1
           The first byte of the signature
@param b2
           The second byte of the signature
@param b3
           The third byte of the signature
@param b4
           The fourth byte of the signature
@see #detectEncoding
src/nu/validator/gnu/xml/aelfred2/XmlParser.java