Sync function runs validation and generates access() and channel() maps.

sync.js

config.sync = function(doc, oldDoc, userCtx, secObj) {
  if (doc.channel_id) {
    // doc belongs to a channel
    channel("ch-"+doc.channel_id);
    // this document describes a channel
    if (doc.channel_id == doc._id) {
      // magic document, treat it carefully
      if (oldDoc && oldDoc.owners.indexOf(userCtx.name) === -1) {
        throw({unauthorized:"you are not a channel owner"});
      }
      // grants access to the channel to all members and owners
      access(doc.owners, "ch-"+doc._id);
      access(doc.members, "ch-"+doc._id);
    }
  }
}