title: Regex for excluding a character
body: <p>I am using <code>=@.*?@</code> to find placeholders in a string e.g: <code>=@something@</code>.
  Now i want to forbid any <code>=</code> in between the 2 <code>@</code>. So that this String is not found: <code>=@some=@any@@</code>. </p>