<p>What are some of the lesser know, but important and useful features of Windows batch files?</p>

<p>Guidelines:</p>

<ul>
<li>One feature per answer</li>
<li>Give both a short <strong>description</strong> of the feature and an <strong>example</strong>, not just a link to documentation</li>
<li>Limit answers to <strong>native funtionality</strong>, i.e., does not require additional software, like the <em>Windows Resource Kit</em></li>
</ul>

<p>Clarification: We refer here to scripts that are processed by cmd.exe, which is the default on WinNT variants.</p>

<p>(See also: <a href="https://stackoverflow.com/questions/148968/windows-batch-files-bat-vs-cmd">Windows batch files: .bat vs .cmd?</a>)</p>

I have always found it difficult to read comments that are marked by a keyword on each line:
```
```
REM blah blah blah
```
```
Easier to read:
```
```
:: blah blah blah
```
```