Partial HTML encoder

Suppose I have text with HTML tags, but where not all characters have been encoded. Are there any tools to intelligently encode while leaving the tags intact? Example:

&l开发者_Go百科t;h2>A'b</h2>

to

<h2>A&#39;b-</h2>

You could give HTML Tidy a shot... Im not sure if you can configure it to do only this though...