SAP ABAP LANGUAGE MODULARIZATION documentation, setup help and example usage

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Modularization Statements
Each ABAP program is divided into processing blocks . Each accessible statement of an ABAP program that does not belong to the global declaration section of the program belongs to a processing block . The possible processing blocks are:

Procedures

You use ABAP statements to call their processing. Possible procedures are methods , function modules, and subroutines .

Dialog modules

You use the flow logic to call their processing.

Event block

Their processing is triggered by events in the ABAP runtime environment .
You can define the processing blocks in any order in the source text of the ABAP program. Non-declarative statements that appear between or after closed processing blocks cannot be accessed and can never be executed. The syntax check reports such dead coding as an error. Declarative statements that appear between or after closed processing blocks belong to the global data declarations of the ABAP program and are visible in all subsequent processing blocks.
You can also use macros and include programs to modularize a source text beyond the use of processing blocks.