@Override
	public int childOffset() {
		return _nodes.childOffsets[_index];
	}
Return the index of the first child node in the underlying node array.
{@code -1} is returned if {@code this} node is a leaf.

@return Return the index of the first child node in the underlying node
        array, or {@code -1} if {@code this} node is a leaf
jenetics.ext/src/main/java/io/jenetics/ext/util/FlatTreeNode.java