Scope and Visibility

Scope

The scope of an identifier is a part of the program in which the identifier can be used to access its object. There are different categories of scope, which depends on how and where identifiers are declared:

Place of declaration	Scope
Identifier is declared in the declaration section of the main module, out of any function or procedure	Scope extends from the point where it is declared to the end of the current file, including all routines enclosed within that scope. These identifiers have a file scope and are referred to as globals.
Identifier is declared in the function or procedure	Scope extends from the point where it is declared to the end of the current routine. These identifiers are referred to as locals.
Identifier is declared in the interface section of the module	Scope extends the interface section of a module from the point where it is declared to the end of the module, and to any other module or program that uses that module. The only exception are symbols which have a scope limited to the file in which they are declared.
Identifier is declared in the implementation section of the module, but not within any function or procedure	Scope extends from the point where it is declared to the end of the module. The identifier is available to any function or procedure in the module.

Visibility

The visibility of an identifier is that region of the program source code from which legal access to the identifier’s associated object can be made.

Scope and visibility usually coincide, though there are circumstances under which an object becomes temporarily hidden by the appearance of a duplicate identifier, i.e. the object still exists but the original identifier cannot be used to access it until the scope of the duplicate identifier is ended.

Technically, visibility cannot exceed scope, but scope can exceed visibility.

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