Why is textarea filled with mysterious white spaces?

Question

I have a simple text area in a form like this:

    <?php if(         
<script async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script>
<ins class="adsbygoogle"
     style="display:block"
     data-ad-client="ca-pub-5408099190056760"
     data-ad-slot="7305827575"
     data-ad-format="auto"
     data-full-width-responsive="true"></ins>
<script>
     (adsbygoogle = window.adsbygoogle || []).push({});
</script>        </div>
      </div>
      
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                <span>(楼主)</span>
            
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                <span>2020-11-28 02:21</span>
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              <p>          
<p>In short: 
<code><textarea></code> should be closed immediately on the same line where it started.</p>

<hr>

<p><strong>General Practice:</strong> this will add-up line-breaks and spaces used for indentation in the code.</p>

<pre><code><textarea id="sitelink" name="sitelink">

Correct Practice