Regular expression, a simple example of replacing all HTML tags

I wrote a regular expression myself, <(.|n)+?>

This is to replace all HTML tags, non-greedy, multi-line.

If I want to replace all non-HTML tags,

My code can only be like this, first find the HTML tag, and then replace the tag.

Can I find non-HTML tags directly? .

There is another problem, intercepting the length of the string.

The method I used below does not determine whether it is Chinese or non-Chinese. The intercepted length is always longer or shorter.

I don’t know if there is a better way to make the intercepted length the same length, instead of the length of str.Length.

public static string formatString(string str, int size)
    {
      string temp = str;
 
      Regex regex = new Regex("<.+?>");
 
      temp = regex.Replace(str, "");
 
      temp = temp.Replace("\r\n", "");
 
      temp = temp.Replace(" ", "");
 
      if (temp.Length >= size)
      {
        temp = temp.Substring(0, size - 3) + " ";
      }
 
      return temp;
    }