IF,ELSE, ENDIF

    Define if block. Can be nested. Note that `THEN' is not needed. The ELSE clause may be absent. More complicated forms of logical expressions including `and'/`or' are not ready yet. IF a rel b ;
;
ELSE ;
;
ENDIF ;

a, b

Expressions.

rel

A relational operator.  One of =, &#;'74, &#;'76, &#;'74=, &#;'76=, =&#;'74, =&#;'76, &#;'74, &#;'76.

Do not forget ``;''.