Determining that a string is a valid HTML element - php

Question

I'm having trouble getting this constraint matches function to match all HTML elements.
It must return true for any legitimate, properly-formed HTML element and return false for anything that is not a legitimate, properly-formed HTML element.
The following are things that did not work:
$dom = new \DOMDocument(); return $dom->loadHTML($value);
$dom = new \DOMDocument(); return $dom->loadHTML($value,LIBXML_HTML_NOIMPLIED);
Adding the flag LIBXML_NOENT to simplexml_load_string().
Adding the flag LIBXML_HTML_NOIMPLIED to simplexml_load_string().
Here is the current function:
function matches($value)
{
\libxml_use_internal_errors(true);
if (!\is_string($value) || empty($value)) {
return false;
}
$start = \strpos($value, '<');
$end = \strrpos($value, '>', $start);
$len = \strlen($value);
if ($end !== false) {
$value = \substr($value, $start);
} else {
$value = \substr($value, $start, $len - $start);
}
$value = \html_entity_decode($value);
$value = \str_replace('&', '', $value);
\libxml_clear_errors();
$xml = \simplexml_load_string($value);
return \count(\libxml_get_errors()) === 0;
}
The current version has two known problems:
<script>&</script>: Should fail but passes.
<a b="""></a>: Should pass but fails.