some questions about mesh network

[Captain_RB]

I'm learning MESH_DEMO of esp8266,but I have some tough problems which confuse me some days badly.
I know in a mesh network there is only one root node and many other childnodes,the childnodes could communicate with each other over their parent's AP.When I am setting up a mesh network, I choose only one node as root which use MESH_LOCAL to enable mesh,and the others use MESH_ONLINE. In mesh network,every nodes could send mesh package to the others which are also in mesh network,in the meanwhile the others could parse the mesh package and do next work. As for the server,it works as a platform which provides user with control and information interactions ,if I don’t need the server,I could discard it,the mesh network could also operate normally.

QUESTIONS:
1、Is my understanding and operations correct?
2、I have browsed your rely message on Espressif forum ,you said "MESH_LOCAL means that the root connect router and doesn't setup TCP connection with server; MESH_ONLINE means that the node connect parent AP or router AP and setup TCP connection with parent or server", but I wonder why only childnode can communicate with server ,and I am still confused about the difference between MESH_AP and MESH_LOCAL, does MESH_AP mean it won't join router?

3、For every mesh node, they can send mesh package which means the format must include mesh header, then the receiver can parse the message. I wonder if the mesh node can only send package in mesh format? If I send normal massage, does the mesh nodes work normally?