title: What opaque content exactly mean?
body: <p><a href="http://docs.oracle.com/javase/7/docs/api/java/nio/file/attribute/BasicFileAttributes.html#isRegularFile%28%29" rel="noreferrer">Here</a> we have the description of <code>isRegularFile()</code> method of the <code>BasicFileAttributes</code> interface:</p>
  
  <blockquote>
    <p>Tells whether the file is a regular file with opaque content.</p>
  </blockquote>
  
  <p>What do they mean by "opaque content", not visible? and if so, does it mean that a file with transparent content is not a regular file?
  Thanks in advance.</p>