title: When we use declare and export keyword in TypeScript?
body: <p>In ts file I see declaration of interface:</p>
  
  <pre><code>declare interface BlockForm {
  }
  </code></pre>
  
  <p>But in others places I see declaration as:</p>
  
  <pre><code>export interface BlockFormField {
  }
  </code></pre>
  
  <p>What is difference, when we should use declare interface and export interface?</p>