public void startDocument(String encoding, Boolean standalone) throws IOException,
            IllegalArgumentException, IllegalStateException {
        append("<?xml version='1.0' encoding='utf-8' standalone='"
                + (standalone ? "yes" : "no") + "' ?>\n");
        mLineStart = true;
    }
Allocate a FastXmlSerializer with the given internal output buffer size.  If the
size is zero or negative, then the default buffer size will be used.

@param bufferSize Size in bytes of the in-memory output buffer that the writer will use.
android/android_framework/base/src/main/java/github/tornaco/android/thanos/core/util/FastXmlSerializer.java