When one block encloses another, the former is called the outer block and the latter the inner block. If an identifier declared in an outer block is redeclared in an inner block, the inner declaration takes precedence over the outer one and determines the meaning of the identifier for the duration of the inner block. For example, if you declare a variable called MaxValue in the interface section of a unit, and then declare another variable with the same name in a function declaration within that unit, any unqualified occurrences of MaxValue in the function block are governed by the second, local declaration. Similarly, a function declared within another function creates a new, inner scope in which identifiers used by the outer function can be redeclared locally.
The use of multiple units further complicates the definition of scope. Each unit listed in a uses clause imposes a new scope that encloses the remaining units used and the program or unit containing the uses clause. The first unit in a uses clause represents the outermost scope and each succeeding unit represents a new scope inside the previous one. If two or more units declare the same identifier in their interface sections, an unqualified reference to the identifier selects the declaration in the innermost scope, that is, in the unit where the reference itself occurs, or, if that unit doesn't declare the identifier, in the last unit in the uses clause that does declare the identifier.
The System and Sysinit units are used automatically by every program or unit. The declarations in System, along with the predefined types, routines, and constants that the compiler understands automatically, always have the outermost scope.
You can override these rules of scope and bypass an inner declaration by using a qualified identifier (see Qualified Identifiers) or a with statement (see With Statements, above).
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