title: how to insert contents to beginning and end of a visual block using vim scripting
body: <p>I am new to vim scripting. Is it possible to do the following using <strong>vim scripting</strong>?</p>
  
  <p>I have a visual block of text. By pressing function key (say F5) I need to insert some text to beginning and end of my visual block.</p>
  
  <p>i.e. the following text is in visual block:</p>
  
  <p><strong>Lorem ipusm doret lorem ipsum. Lorem ipusm doret lorem ipsum. Lorem ipusm doret lorem ipsum. Lorem Lorem ipusm doret lorem ipsum.</strong> </p>
  
  <p><strong>Lorem ipusm doret lorem ipsum. Lorem ipusm doret lorem ipsum. Lorem ipusm doret lorem ipsum. Ipusm doret lorem ipsum.</strong></p>
  
  <p>On pressing F5 key, the text should be changed to:</p>
  
  <p><strong>"[[Lorem ipusm doret lorem ipsum. Lorem ipusm doret lorem ipsum. Lorem ipusm doret lorem ipsum. Lorem Lorem ipusm doret lorem ipsum.</strong> </p>
  
  <p><strong>Lorem ipusm doret lorem ipsum. Lorem ipusm doret lorem ipsum. Lorem ipusm doret lorem ipsum. Ipusm doret lorem ipsum.]]"</strong></p>
  
  <p>The text <strong>"[[</strong> and <strong>]]"</strong> needs to be placed on beginning and end of the visual block. Can anybody give me a solution for this.</p>