Using PHP regex, how can I removed HTML tags (both opening and closing) and with attributes like `<hr class="myclass" />` without removing non HTML tags like `<dog>` or `<dog class="cat">`?

The non HTML tags are dynamic and cannot be hard coded.

Input:

```
<b><> <<> <dog> <123> <" !> <!--...--> <!doctype> <hr class="myclass" /> </b>

```

Output should be:

```
<> <<> <dog> <123> <" !>

```

I'm considering to use HTML Purifier but first I need to know if this is possible in regex.

HTML Tag reference: <http://www.quackit.com/html/tags/>

Thanks in advance =)