title: Python Cerberus: multipe schemas for a single filed?
body: <p>I am trying to use Cerberus to validate some data but I run into a problem.</p>
  
  <p>I defined several smaller schema such as:</p>
  
  <pre><code>A = {"type": "dict", "required": False, "schema": {"name": {"type": "string"}}}
  
  B = {"type": "dict", "required": False, "schema": {"age": {"type": "integer"}}}
  
  C = {"type": "dict", "required": False, "schema": {"gender": {"type": "string"}}}
  </code></pre>
  
  <p>And the higher level schema is like:</p>
  
  <pre><code>{"something": {"type": "list", "schema": "type": [A, B, C]}}
  </code></pre>
  
  <p>This obviously doesn't work.</p>
  
  <p>I want to validate a list, the elements in which only need to be validated by one of <code>(A, B, C)</code>. I don't know how to do that with Cerberus and am looking for some help.</p>
  
  <p>Thanks.</p>