Here is a list of all enums with links to the classes they belong to:

alignment : dx::circular::format
bitmap : dx::stream::clock
bus : dx::stream::desc< target_t, max_streams, max_pins, max_clock_settings, max_clocks, max_configurations >
direction : dx::usb::__request_type, dxd::usb_device::pipe
endian : dx::circular::format
eumb : dxd::ppc
host_property_key : dxd::fw
i2o : dxd::ppc
level : dx::log
plug : dx::stream::desc< target_t, max_streams, max_pins, max_clock_settings, max_clocks, max_configurations >::stream::pin
priority : dxd::process
recipient : dx::usb::__request_type
request : dx::usb::control
speed : dx::usb::platform::device, dxd::usb_device
synchronization : dx::usb::pipe< device_t >::attributes
transfer : dx::usb::pipe< device_t >::attributes
type : dx::stream::encoder::index, dx::usb::__request_type, dx::usb::platform::pipe< device_t, interface_t >, dxd::usb_device::pipe
usage : dx::usb::pipe< device_t >::attributes