How can I replace strings NOT within a link tag?

Question

I am working on this PHP function. The idea is to wrap certain words occuring in a string into certain tags (both, words and tags, given in an array). It works OK!, but when

Answer 1

Definitely use a dom parser to isolate the qualifying text nodes before attempting to replace with a regex pattern that respects: word boundries, case-insensitivity, and unicode characters. If you are planning to specifically target words with unicode characters, then you will need to add mb_ to some of the string functions.

After leveraging the following insights, I tailored a solution for your scenario.

• https://stackoverflow.com/a/64077957/2943403
• https://stackoverflow.com/a/20675396/2943403

Code: (Demo)

$html = <<fóo lórem
bár ipsum bar food foo bark. bar not á test
HTML;

$lookup = [
    'foo' => 'h3',
    'bar' => 'h2'
];

libxml_use_internal_errors(true);
$dom = new DOMDocument();
$dom->loadHTML($html, LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD);

$xpath = new DOMXPath($dom);

$regexNeedles = [];
foreach ($lookup as $word => $tagName) {
    $regexNeedles[] = preg_quote($word, '~');
}
$pattern = '~\b(' . implode('|', $regexNeedles) . ')\b~iu' ;

foreach($xpath->query('//*[not(self::a)]/text()') as $textNode) {
    $newNodes = [];
    $hasReplacement = false;
    foreach (preg_split($pattern, $textNode->nodeValue, 0, PREG_SPLIT_NO_EMPTY | PREG_SPLIT_DELIM_CAPTURE) as $fragment) {
        $fragmentLower = strtolower($fragment);
        if (isset($lookup[$fragmentLower])) {
            $hasReplacement = true;
            $a = $dom->createElement($lookup[$fragmentLower]);
            $a->nodeValue = $fragment;
            $newNodes[] = $a;
        } else {
            $newNodes[] = $dom->createTextNode($fragment);
        }
    }
    if ($hasReplacement) {
        $newFragment = $dom->createDocumentFragment();
        foreach ($newNodes as $newNode) {
            $newFragment->appendChild($newNode);
        }
        $textNode->parentNode->replaceChild($newFragment, $textNode);
    }
}
echo substr(trim(utf8_decode($dom->saveHTML($dom->documentElement))), 3, -4);

Output:

foo
 fóo lórem
bár ipsum 
bar
 food 
foo
 bark. bar not á test