The enumerating SUBs are used in a similar way as the structure type SUBs.
A common use for those enumerated variables are the definition of object
types, return values, error numbers etc.

Example: (defining some return values)
--------------------------------------
    SetENUM 0&
    IncEVAR RETURN_OK&
    IncEVAR RETURN_WARN&
    IncEVAR RETURN_ERROR&
    IncEVAR RETURN_FAIL&

and again with explaination:
----------------------------
    SetENUM 0&
      'this SUB does init the enumerating base number

    IncEVAR RETURN_OK&
      'set the variable RETURN_OK& = offset counter (is zero from the init above)
      'increment the offset counter by 1 for the next variable

    IncEVAR RETURN_WARN&
      'set the variable RETURN_WARN& = offset counter (now 1 from last increment)
      'increment the offset counter by 1 for the next variable

    IncEVAR RETURN_ERROR&
      'set the variable RETURN_ERROR& = offset counter (now 2 from last increment)
      'increment the offset counter by 1 for the next variable

    IncEVAR RETURN_FAIL&
      'set the variable RETURN_FAIL& = offset counter (now 3 from last increment)
      'increment the offset counter by 1 for the next variable

Another Example: (separating the OK value from error levels by setting
a new base in between, you may set a new base at any time)
----------------------------------------------------------------------
    SetENUM 0&
    IncEVAR RETURN_OK&
    SetENUM 10&
    IncEVAR RETURN_WARN&
    IncEVAR RETURN_ERROR&
    IncEVAR RETURN_FAIL&

and once again with explaination:
---------------------------------
    SetENUM 0&
      'this SUB does init the enumerating base number

    IncEVAR RETURN_OK&
      'set the variable RETURN_OK& = offset counter (is zero from the init above)
      'increment the offset counter by 1 for the next variable

    SetENUM 10&
      'init a new enumerating base number

    IncEVAR RETURN_WARN&
      'set the variable RETURN_WARN& = offset counter (is 10 from the new base init)
      'increment the offset counter by 1 for the next variable

    IncEVAR RETURN_ERROR&
      'set the variable RETURN_ERROR& = offset counter (now 11 from last increment)
      'increment the offset counter by 1 for the next variable

    IncEVAR RETURN_FAIL&
      'set the variable RETURN_FAIL& = offset counter (now 12 from last increment)
      'increment the offset counter by 1 for the next variable

Likewise you could use DecEVAR to generate decrementing variable numbers.
Mixing IncEVAR and DecEVAR in the same sequence seems useless.

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