title: Tokenfield - allow only tokens from source
body: <p>I'm trying to use Tokenfield plugin - <a href="http://sliptree.github.io/bootstrap-tokenfield" rel="nofollow">http://sliptree.github.io/bootstrap-tokenfield</a></p>
  
  <p>How can I restrict use only tokens from source? </p>
  
  <pre><code>$('#tokenfield_platform').tokenfield({
  autocomplete: {
  source: [
          {% for platform_item in platforms %}
          '{{ platform_item }}',
      {% endfor %}
  ],
  delay: 100
  },
  createTokensOnBlur:true,
  showAutocompleteOnFocus: true
  }).on('tokenfield:createtoken', function (event) {
      var existingTokens = $(this).tokenfield('getTokens');
      $.each(existingTokens, function(index, token) {
      if (token.value === event.attrs.value)
          event.preventDefault();
      });
      //var available_tokens = bloodhound_tokens.index.datums;
      // I do not want to use Twitter Typeahead, but only tokens from source
      var exists = true;
      $.each([available_tokens, function(index, token) {
      if (token.value === event.attrs.value)
          exists = false;
      });
      if(exists === true)
      event.preventDefault();
  });
  </code></pre>
  
  <p>Thanks for any info.</p>