Hi Allen,
Windows is only meant as an example of a group. Nothing is stopping you from organizing your inventory like this, for example:
[clients]
client1
[servers]
server1
However, since Windows nodes require a winrm connection, you need to specify that for all windows nodes so that Ansible is aware of the fact that the node is running windows. You can do this in several ways:
option 1, continuing from the example above:
[clients]
client1
[servers]
server1
[clients:vars]
ansible_connection=winrm
[servers:vars]
ansible_connection=winrm
A more flexible approach is to have a "top-level" group where the common vars are stored, and then have your two groups "inherit" from that:
[windows]
[windows:children]
clients
servers
[clients]
client1
[servers]
server1
[windows:vars]
ansible_connection=winrm
again, the group name "windows" is just an example, it can be anything you like.