The IF command makes it possible to execute some commands conditionally.
The format of the command is:
IF condition THEN
commands
[ ELSEIF condition THEN
commands
]*
[ ELSE
commands ]
ENDIF
The ELSEIF part is conditional, need not present and there can be many of
it in a single IF command. Similarly the ELSE part is also optional
but there can only be one ELSE part.
Note that the keyword ELSEIF is a single keyword and it is syntactically
incorrect to write ELSE IF in two words.
The condition can be any expression that evaluates to a boolean value. There
is no automatic conversion from non boolean values to boolean value.
