Scope is a context within which to resolve names to values.

Tcl has many scopes:

'''namespace''' is an hierarchal scope for resolving names of [commands] and [variables].  The [variable] command references a variable name in namespace scope.

'''global''' scope is a distinguished namespace scope, equivalent to namespace :: in some interpreter

'''hidden''' scope is a per-interpreter scope for [interp] hidden commands

'''call frame''' scope is the context of some call frame in the current evaluation.

'''proc local''' scope is the context within which all otherwise unqualified variable names referenced in a [proc] are defined.  Proc local is a special case of a call frame scope, being the nearest enclosing call frame scope.

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In summary, there are two major kinds of scoping in tcl - dynamic and lexical (or static) scope.

'''dynamic''' scope is accessed by default inside a proc, or by means of [upvar] with unqualified names, and is preferred for variable name resolution.

'''static''' or '''lexical''' scope is accessed explicitly by namespace encoded names, the [global] operator, and implicitly by [command invocation] and by the [variable] operator.  Command resolution prefers dynamic scope.

[RS] has learnt this distinction, however:
   * '''dynamic scope''' determines variable value at runtime - used in older [Lisp] versions
   * '''lexical scope''' conserves the value of variables they had at the time a [proc] was defined, for instance in [closures] - considered more advanced in [Lisp] circles

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[Category Concept]