private boolean isPreamble(int index) {
        if (index <= buffer.length() - 6) {
            if (
                    buffer.get(index)     == '<' && 
                    buffer.get(index + 1) == '?' && 
                    buffer.get(index + 2) == 'x' && 
                    buffer.get(index + 3) == 'm' && 
                    buffer.get(index + 4) == 'l' && 
                    buffer.get(index + 5) == ' '
                ) {
                return true;
            }
        }
        return false;
    }
Returns true if the index points to an XML preamble of the following example form:

<pre>
  &lt;?xml version="1.0"?>
</pre>
@param index
gateway/engine/core/src/main/java/io/apiman/gateway/engine/soap/SoapHeaderScanner.java