protected void encodeThis(ByteBuffer buffer) {
        super.encodeThis(buffer);
        putString(index, buffer);
    }
The *full* name of the field searched by this,
which is prefixed by the parent name and a dot if this is inside a SameElement,
and the same as getIndexName otherwise.
container-search/src/main/java/com/yahoo/prelude/query/SimpleIndexedItem.java