The Cluster Name can either be explicitly specified when the item is called or displayed, or an item can use the default cluster context of the calling process or page. If your system has only one cluster, you don't need to specify a cluster name. Single cluster systems always use that cluster and will not require the use of cluster prefixes.
Cluster context, therefore, is the default cluster used for tag resolution and execution of expressions and Cicode functions. Citect SCADA will automatically resolve tags without a cluster context if every tag name in the project is unique.
In the case of tags and tag references, a cluster is explicitly supplied by prefixing the tag name or tag reference with the cluster name. For built-in Cicode functions ClusterName is usually an optional parameter. Variable Tags referenced in an Alarms, Reports or Trends Server context are implicitly resolved to that cluster unless explicitly stated otherwise using a cluster prefix such as ClusterName.TagName.
Server processes (Alarm, Trend, Report) have their default cluster context set to their own cluster, so that, for example, Alarm definitions that contain variable tags without clusters explicitly supplied will attempt to resolve those tags to their own cluster. Cicode tasks started from server code will inherit the servers cluster unless one is explicitly given. For built-in Cicode functions ClusterName is usually an optional parameter.
Graphics pages have no cluster context by default. A page's cluster can be supplied statically in the page appearance properties, can be inherited from a previous context, or can be applied dynamically using an optional parameter in the Cicode function that displayed the page. Any Cicode tasks started from a page will inherit the cluster context of that page. Graphics pages have no default cluster and will not inherit context in multi-cluster systems by default.
The TaskNew Cicode function inherits the caller's (either page or task) cluster context unless explicitly overridden.