title: ANTLR: call a rule from a different grammar
body: <p>is it possible to invoke a rule from a different grammar? <br>
  the purpose is to have two languages in the same file, the second language starting by an (begin ...) where ... is in the second language. the grammar should invoke another grammar to parse that second language.</p>
  
  <p>for example:</p>
  
  <pre><code>
  grammar A;
  
  start_rule
      :    '(' 'begin' B.program ')' //or something like that
      ;
  
  </code></pre>
  
  <pre><code>
  grammar B;
  
  program
      :   something* EOF
      ;
  
  something
      : ...
      ;
  </code></pre>