Clarified the sync document

docs/sync.markdown

@@ -17,19 +17,21 b' Protocol version is the version of the s'
 of data models. If at least one of them is different, the sync cannot be
 performed.
 
-The node signs the data with its key. The receiving node saves the key at the
+The node signs the data with its keys. The receiving node saves the key at the
 first sync and checks it every time. If the key has changed, the info won't be
-saved from the node (or the node id must be changed).
+saved from the node (or the node id must be changed). A model can be signed 
+with several keys but at least one of them must be the same as in the global 
+ID to verify the sender.
 
 Each node can have several keys. Nodes can have shared keys to serve as a pool
 (several nodes with the same key).
 
-Each post has an ID in the unique format: node-id/post-id
+Each post has an ID in the unique format: [key-type][key][local-id]
 
-All requests pass a request type, protocol and model versions and a list of
+All requests pass a request type, protocol and model versions, and a list of
 optional arguments used for filtering.
 
-Each protocol has its own version. Version consists of 2 numbers: first is
+Each request has its own version. Version consists of 2 numbers: first is
 incompatible version (1.3 and 2.0 are not compatible and must not be in sync)
 and the second one is minor and compatible (for example, new optional field
 is added which will be igroned by those who don't support it yet).