is it possible to process html to auto close tags with no close tags?

i have this string

<div>
  <p><strong>Elem_A</strong>String_A2_2 <String_A2_2> asdas</p>
  <p><strong>Elem_B</strong>String_B2_2 String_B2_2</p>
</div>

and i want to covert it to

<div>
  <p><strong>Elem_A</strong>String_A2_2 <String_A2_2/> asdas</p>
  <开发者_StackOverflowp><strong>Elem_B</strong>String_B2_2 String_B2_2</p>
</div>

basically i want to autoclose any non html known tag , because i have problems with processing this html in htmlagilitypack as it changes the meaning of the html.

HTML (meaning not XHTML) already does this: auto closed tags are defined without a trailing closing / (<br>).

I'm not familiar with htmlagilitypack, but if you make your own DTD based on HTML4.01, extended with your own tag, then there must be some HTML parser that can work.