This Regular Expression removes all attributes and values from an HTML tag, preserving the tag itself and textual content (if found).

strip_tag_attribs.md

Strip HTML Attributes

<([a-z][a-z0-9]*)[^>]*?(/?)>

token	explanation
<	match < at beginning of tags
(	start capture group $1 - tag name
[a-z]	match a through z
[a-z0-9]*	match a through z or 0 through 9 zero or more times
)	end capture group
[^>]*?	match anything other than >, zero or more times, not-greedy (wont eat the /)
(/?)	capture group $2 - / if it is there
>	match >

Add some quoting, and use the replacement text <$1$2> it should strip any text after the tagname until the end of tag /> or just >.

Example

Before

HTML containing style attributes.

<p style="padding:0px;">
	<strong style="padding:0;margin:0;">hello</strong>
</p>

After

HTML attributes removed.

<p>
	<strong>hello</strong>
</p>

PHP Example

$with_attr    = '<p style="padding:0px;"><strong style="padding:0;margin:0;">hello</strong></p>';
$without_attr = preg_replace("/<([a-z][a-z0-9]*)[^>]*?(/?)>/i",'<$1$2>', $with_attr);

echo $without_attr
<p><strong>hello</strong></p>

stackoverflow post.

I'll answer myself. Here's how to remove html tags and put them back again: https://gist.github.com/miguelgisbert/7ef9ee15aa0cc1ba32ea5ed192e486c3

    $str1 = "<p style='color:red;'>red</p><strong style='color:green;'>green</strong>";
    $pattern = '/<[^>]+>/';

    preg_match_all($pattern, $str1, $matches);
    $replacements = $matches[0];
    $str2 = preg_replace($pattern, '<>', $str1);

    // TRanslate $str2 with DeepL or do whatever without html tags

    $str3 = preg_replace_callback('/<>/', function($matches) use (&$replacements) {
        return array_shift($replacements);
    }, $str2);

    echo "str1 ".$str1."<br>";
    echo "str2 ".$str2."<br>";
    echo "str3 ".$str3."<br>";