I didn't test the logic used in this page - http://www.phpro.org/examples/Get-Text-Between-Tags.html But I can confirm the logical point made at the top of the page in big bold letters that says you shouldn't do what you're trying to do with regex.
Html is not uniform and edge cases will always bite you in the rear if you use regular expressions to handle the content of those tags in any real world situation. So unless your markup is extremely simplistic, uniform, 100% accurate, only contains html (not css, javascript or garbage) then your best bet is a dom parser library.
And really many dom parser libraries have problems too but you'll be miles ahead of the regex counterparts. The best way to get the text contet of tags is to render the html in a browser and access the innerText property of the given dom node (or have a human copy and paste the contents out manually) - but that isn't always an option :D