> | III.10 Conditional Assembly Conditional assembly allows to assemble or ignore selected parts of code. This can be used to keep the code for various program variants in a single source, to ease configuration control and maintenance. Conditional assembly is also useful to write fancy macros. The following fourteen meta instructions have been implemented:
>     IF     <expr>            ELSEIF     <expr>
>     IFN    <expr>            ELSEIFN    <expr>
>     IFDEF  <symbol>          ELSEIFDEF  <symbol>
>     IFNDEF <symbol>          ELSEIFNDEF <symbol>
>     IFB    <literal>         ELSEIFB    <literal>
>     IFNB   <literal>         ELSEIFNB   <literal>
>     ENDIF                    ELSE
Meta instructions overlay the Intel MCS-51 assembly language, but are not part of it! C programmers may compare them to C preprocessor commands. In the subsequent text, IFxx is used as a collective name for the IF/IFN/IFDEF/IFNDEF/IFB/IFNB instructions. In analogy ELSEIFxx is used as a collective name for the ELSEIF/ELSEIFN/ELSEIFDEF/ELSEIFNDEF/ELSEIFB/ELSEIFNB instructions (not including ELSE). General IFxx Construction IFxx and ELSEIFxx Instructions