title: Assign meaning to text (ValidID) in xtext editor
body: <p>This might be very basic question but: how to assign meaning to text in xtext editor?</p>
  
  <p>Let's say:</p>
  
  <p>We have an instance of some Java object. Let's name it Data. This data object has several nested fields which contain data.</p>
  
  <pre><code>data.field1.value1, 
  data.field1.value2, 
  data.value1, 
  etc...
  </code></pre>
  
  <p>Data object is created at runtime by user input and will be available when xtext based editor would try to access it.</p>
  
  <p>If I write in xtext editor text like: </p>
  
  <pre><code>data.field1.value1
  </code></pre>
  
  <p>how to bind it to that field of data object?</p>
  
  <p>To clarify: "data" object comes from outside of xtext editor but is accessible for the editor but I don't know how and where to pass it and then how to bind "ValidID" rule to its fields.</p>