Convert HTML special characters to HTML entities preserving HTML entities

This function simply converts HTML special characters to their HTML entities, while preserving already existing HTML entities. It uses the HTML translation table for the convertion.

So if you have a sentence including HTML special characters and HTML entities, it will be parsed as the HTML entities, so no markup will be performed.

<?php
/**
 * htmlspecialchars2()
 * Converts special characters to HTML entities
 * Prereserves already existing HTML entities
 * @param mixed $string string to be manipulated
 * @param mixed $quote quote convertion style
 * @return string $string
 */
function htmlspecialchars2($string, $quote = ENT_QUOTES){
    if (!is_string($string))
        return;

    $specialchars = get_html_translation_table(HTML_SPECIALCHARS, $quote);

    foreach ($specialchars as $char => $entitie)
        if (preg_match("@{$entitie}@si", $string)){
            $string = preg_replace("@{$entitie}@", $char, $string);
        }

    return strtr($string, $specialchars);
}

// Preserving HTML entities
echo htmlspecialchars2('<em>Italic!</em> <strong>Bold text!</strong> & &lt;strong&gt;Bold text again!&lt;/strong&gt;');
echo "<br />\n";
// Original PHP
echo htmlspecialchars('<em>Italic!</em> <strong>Bold text!</strong> & &lt;strong&gt;Bold text again!&lt;/strong&gt;');
?>

This is the output of the above snippet:

<em>Italic!</em> <strong>Bold text!</strong> & <strong>Bold text again!</strong>

<em>Italic!</em> <strong>Bold text!</strong> & &lt;strong&gt;Bold text again!&lt;/strong&gt;

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