title: How to provide custom string placeholder for string format
body: <p>I have a string </p>
  
  <pre><code>string str ="Enter {0} patient name";
  </code></pre>
  
  <p>I am using string.format to format it.</p>
  
  <pre><code>String.Format(str, "Hello");
  </code></pre>
  
  <p>Now if i want patient also to be retrieved from some config then I need to change str to something like
  <code>"Enter {0} {1} name"</code>. So it will replace the {1} with second value. The problem is that I want instead of {1} some other format something like <code>{pat}</code>. But when I try to use, it throws an error. The reason I want a different format is that there are lot of files I need to change like this(which may contain {0},{1} etc). So I need a custom placeholder which can be replaced at run-time.</p>