title: What's the purpose of _tags file with OCaml, and how to interpret the contents?
body: <p>From <a href="https://stackoverflow.com/questions/28751359/building-ocaml-code-that-uses-list-comprehension">Building OCaml code that uses list comprehension</a> post, I can use <code>_tags</code> file to execute <code>ocamlbuild</code> with less build options. </p>
  
  <pre><code>$ cat _tags
  &lt;**/*&gt; : package(camlp4),syntax(camlp4o),package(pa_comprehension)
  </code></pre>
  
  <p>From the <a href="https://github.com/ocaml-batteries-team/batteries-included/wiki/Getting-started" rel="nofollow noreferrer">Batteries introduction</a>, I also need to have _tags file to use Batteries package.</p>
  
  <pre><code>&lt;*&gt;: package(batteries)
  </code></pre>
  
  <p>Why the first example uses <code>&lt;**/*&gt;</code> when the second example uses <code>&lt;*&gt;</code>? In general, what's the purpose of _tags file in ocamlbuild? Do you have some good tutorials on it? </p>