public static string md(this string s) {
bool e = false, b = false;
Buffer sb = new Buffer(s);
for (int i=1;i<s.Length;++i) {
var t = s[i];
if (marks.IndexOf(t)<0) continue;
var r = (string) s[i-1];
if (r==@"\") continue;
if (t!='*' || t!='_') continue; // for now
if ((r=="*" && t=='*')) {
b = !b;
} else if (t=='*') e = !e;
} return sb.ToString();
}