In the context of PHP, how can URL encoding impact the extraction of keywords from HTTP_REFERER URLs?

When extracting keywords from HTTP_REFERER URLs in PHP, it's important to decode the URL encoding to ensure accurate keyword extraction. URL encoding can impact the readability of the URL, making it difficult to extract keywords if not properly decoded. To solve this issue, use the `urldecode()` function in PHP to decode the URL encoding before extracting keywords.

$referer_url = $_SERVER['HTTP_REFERER'];
$decoded_url = urldecode($referer_url);
// Extract keywords from $decoded_url