PHP str_ireplace ends html(<p>) tag

Question

str_ireplace with replace ends my html tag.

            $txt = '<p><strong>Add on </strong>[number],<strong> number nr </strong></p>';
            $htmlValue = '<div class="resizing-input"><input type="text" value="1"><span style="display:none"></span></div>';
            $text = str_ireplace('[number]', $htmlValue, $txt);//It needs to be case-insensitive so str_ireplace not str_replace.
            echo'<pre>';print_r($text);echo'</pre>';die;

            //return: <pre><p><strong>Add on </strong></p><div class="resizing-input"><input type="text" value="1"><span style="display:none"></span></div>,<strong> number nr </strong><p></p></pre>

            //should return: <pre><p><strong>Add on </strong><div class="resizing-input"><input type="text" value="1"><span style="display:none"></span></div>,<strong> number nr </strong></p></pre>

Why it does like that?
I want to replace string between [] to html but it ends another html </p> tag. Same thing happens with str_replace too.

Answer 1

The thing is I can't write <div> tag inside a <p> element.
Syntax of the p element does not allow a div child, and the end tag </p> may be omitted, the validator (and a browser) implies </p> when it encounters a <div> tag when parsing ap element. That is, when p is being parsed (or “is open”), the start tag of a div element implicitly closes it.

No p element in scope but ap end tag seen.w3c validation