title: Completely independent Git project within another project using only gitignore
body: <p>Is it possible to work with two <strong>independent</strong> git projects, one within another in the directory tree and separate them using only gitignore (<em>without <a href="https://stackoverflow.com/questions/1811730/how-do-i-work-with-a-git-repository-within-another-repository">submodules</a> or <a href="https://stackoverflow.com/questions/720669/projects-within-projects-using-git">subtrees</a></em>)?</p>
  
  <p>Here is the folder structure:</p>
  
  <pre><code>repo_a     &lt;-- repository A folder
     /.git
     /folder_1
     /folder_2
     /repo_b    &lt;-- repository B folder (to be ignored by repository A)
         /.git
         /folder_3
         /folder_4
  </code></pre>