Why Does DOMDocument Struggle with UTF-8 Characters and How to Fix It?

DOMDocument Struggles with UTF-8 Characters: A Thorough Investigation

DOMDocument, a library in PHP, is designed to handle HTML, which inherently uses the ISO-8859-1 encoding. However, when attempting to load UTF-8 encoded HTML into a DOMDocument instance, the resulting output may exhibit corrupted utf-8 characters.

The Problem:

The example code provided attempts to load the following UTF-8 encoded HTML string:

<code class="html">

    <meta charset="utf-8">
    <title>Test!</title>


    <h1 id="Hello-World">☆ Hello ☆ World ☆</h1>

</code>

However, the output contains HTML entities instead of the intended characters:

<code class="html">
<meta charset="utf-8">
<title>Test!</title>
    <h1 id="amp-acirc-amp-amp-Hello-amp-acirc-amp-amp-World-amp-acirc-amp-amp">&acirc;&#152;&#134; Hello &acirc;&#152;&#134; World &acirc;&#152;&#134;</h1>    
</code>

The Solution:

There are two main approaches to resolve this issue:

1. Converting Characters into HTML Entities:

PHP's mb_convert_encoding function can transform characters outside of the US-ASCII range into their corresponding HTML entities. This ensures that DOMDocument can correctly interpret the string:

<code class="php">$us_ascii = mb_convert_encoding($utf_8, 'HTML-ENTITIES', 'UTF-8');</code>

2. Specifying the Encoding Hint:

DOMDocument can be hinted about the encoding of the HTML string by adding a Content-Type meta tag:

<code class="html"><meta http-equiv="content-type" content="text/html; charset=utf-8"></code>

However, adding the meta tag directly to the HTML string within the code may result in validation errors. To avoid this, you can load the string without the meta tag and use the insertBefore method to add it as the first child of the head element:

<code class="php">$dom = new DomDocument();
$dom->loadHTML($html);
$head = $dom->getElementsByTagName('head')->item(0);
$meta = $dom->createElement('meta');
$meta->setAttribute('http-equiv', 'content-type');
$meta->setAttribute('content', 'text/html; charset=utf-8');
$head->insertBefore($meta, $head->firstChild);
$html = $dom->saveHTML();</code>

By employing either of these methods, DOMDocument can effectively handle UTF-8 encoded HTML, ensuring correct representation and decoding of non-US-ASCII characters.

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