Magento 2: Warning: simplexml_load_string(): Entity: line 1: parser error : XML declaration allowed only at the start of the document

Question

I am using magento 2.0 I have learn magento2 tutorials(No frills magento2 layout) of alan storm. I have create two xml files. when i run controller file then give Following error

Warning: simplexml_load_string(): Entity: line 1: parser error : XML declaration allowed only at the start of the document in C:\wamp\www\magentodemo\vendor\magento\framework\View\Model\Layout\Merge.php on line 488

my xml file is :

top-container.xml

<?xml version="1.0" encoding="UTF-8"?>
 <container name="top" > </container>

block.xml

  <?xml version="1.0" encoding="UTF-8"?>
  <referenceContainer name="top">
<block class="Magento\Framework\View\Element\Template" name="pulsestorm_nofrills_chapter2_block1" template="Pulsestorm_Nofrillslayout :: chapter2/block1.phtml">
</block>
 </referenceContainer>

file locations is

app
  code
     namespace
         modulename
              sample-xml
                -top-container.xml
                -block.xml

Please suggest me