In Version 3 of the SB-Assembler this directive will not perform a boundary sync.
The .EL directive inverts the current test condition. If the current condition was true it will become false. And if it was false it will become true. The following program lines are only assembled if the condition is true until the next .EL directive or until the .FI directive is encountered.
The .EL directive may be used as often as you want to invert the condition between the DO and .FI directives. The condition is inverted every time the .EL directive is used.
The label field of the source line on which the .EL directive is used must be empty. So it's not possible to declare a label on a source line that contains the .EL directive.
.DO 1 Condition is always true (<>0) ; These lines are interpreted by ; the SB-Assembler .EL Reverse condition ; This line is not interpreted .EL Reverse condition ; This line is again interpreted .EL Reverse condition ; This line is again not interpreted .FI End of conditional block