title: PHP embedding array element inside string with curly braces
body: <p>I would like to know what the advantage of using
  curly braces is in the following context:</p>
  
  <pre><code>$world["foo"] = "Foo World!";
  echo "Hello, {$world["foo"]}.\n";
  </code></pre>
  
  <p>is over the following:</p>
  
  <pre><code>$world["foo"] = "Foo World!";
  echo "Hello, $world["foo"].\n";
  </code></pre>
  
  <p>In particular, how is it that the braces resolve any
  possible ambiguity in this case (or similar cases)?</p>