C# to implement the conversion of HTML and UBB to each other

private string DoHtmlToUBB(string _Html)
{

    _Html = (_Html, "<br[^>]*>", "\n");
    _Html = (_Html, @"<p[^>\/]*\/>", "\n");
    _Html = (_Html, "\\son[\\w]{3,16}\\s?=\\s*([\'\"]).+?\\1", "");
    _Html = (_Html, "<hr[^>]*>", "[hr]");

    _Html = (_Html, "<(\\/)?blockquote([^>]*)>", "[$1blockquote]");
    _Html = (_Html, "<img[^>]*smile=\"(\\d+)\"[^>]*>", "'[s:$1]");
    _Html = (_Html, "<img[^>]*src=[\'\"\\s]*([^\\s\'\"]+)[^>]*>", "");
    _Html = (_Html, "<a[^>]*href=[\'\"\\s]*([^\\s\'\"]*)[^>]*>(.+?)<\\/a>", "[url=$1]$2[/url]");
    _Html = (_Html, "<b>(.+?)</b>",@"\[b\]$1\[/b\]");
    _Html = (_Html, "<[^>]*?>", "");
    _Html = (_Html, "&amp;", "&");
    _Html = (_Html, "&nbsp;", " ");
    _Html = (_Html, "&lt;", "<");
    _Html = (_Html, "&gt;", ">");

    return _Html;
}
public string ubbtohtml(string content) //ubb to html
{
    content = (content, @"\r\n", "<br/>");
    content = (content, " ", "&nbsp;");
    content = (content, @"\[b\](.+?)\[/b\]", "<b>$1</b>");
    content = (content, @"\[i\](.+?)\[/i\]", "<i>$1</i>");
    content = (content, @"\[u\](.+?)\[/u\]", "<u>$1</u>");
    content = (content, @"\[p\](.+?)\[/p\]", "<p class='load'>$1</p>");
    content = (content, @"\[align=left\](.+?)\[/align\]", "<align='left'>$1</align>");
    content = (content, @"\[align=center\](.+?)\[/align\]", "<align='center'>$1</align>");
    content = (content, @"\[align=right\](.+?)\[/align\]", "<align='right'>$1</align>");
    content = (content, @"\[url=(?<url>.+?)]\[/url]", "<a href='${url}' target=_blank>${url}</a>");
    content = (content, @"\[url=(?<url>.+?)](?<name>.+?)\[/url]", "<a href='${url}' target=_blank>${name}</a>");
    content = (content, @"\[quote](?<text>.+?)\[/quote]", "<div class="quote">${text}</div>");
    content = (content, @"\[img](?<img>.+?)\[/img]", "<img src='${img}' alt=''/>");
    return content;
}