This is a subtype of the UInt32 DataType with the OptionSetValues Property defined.
It is used to indicate how the Value of a Variable can be accessed (read/write),
if it contains current and/or historic data and its atomicity.
The AccessLevelExType DataType is an extended version of the AccessLevelType DataType and
as such contains the 8 bits of the AccessLevelType as the first 8 bits.
The NonatomicRead, and NonatomicWrite Fields represent the atomicity of a Variable.
In general Atomicity is expected of OPC UA read and write operations.
These Fields are used by systems, in particular hard-realtime controllers, which can not ensure atomicity.
from https://reference.opcfoundation.org/v104/Core/docs/Part3/8.58/:
This is a subtype of the UInt32 DataType with the OptionSetValues Property defined. It is used to indicate how the Value of a Variable can be accessed (read/write), if it contains current and/or historic data and its atomicity. The AccessLevelExType DataType is an extended version of the AccessLevelType DataType and as such contains the 8 bits of the AccessLevelType as the first 8 bits. The NonatomicRead, and NonatomicWrite Fields represent the atomicity of a Variable. In general Atomicity is expected of OPC UA read and write operations. These Fields are used by systems, in particular hard-realtime controllers, which can not ensure atomicity.