Delphi Language Guide Delphi for Microsoft Win32 Delphi for the Microsoft. Net framework

The Implementation Section
The implementation section of a unit begins with the reserved word implementation and continues until the beginning
of the initialization section or, if there is no initialization section, until the end of the unit. The implementation section
defines procedures and functions that are declared in the interface section. Within the implementation section, these
procedures and functions may be defined and called in any order. You can omit parameter lists from public procedure
and function headings when you define them in the implementation section; but if you include a parameter list, it
must match the declaration in the interface section exactly.
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In addition to definitions of public procedures and functions, the implementation section can declare constants, types
(including classes), variables, procedures, and functions that are private to the unit. That is, unlike the interface
section, entities declared in the implementation section are inaccessible to other units.
The implementation section can include its own uses clause, which must appear immediately after the keyword
implementation. The identifiers declared within units specified in the implementation section are only available for
use within the implementation section itself. You cannot refer to such identifiers in the interface section.