This command implements a loop which is repeated so long as long the expression standing after the loop closing line UNTIL becomes true. The loop starts with a line containing the keyword REPEAT and finishes with the line UNTIL expression.
repeat ... commands to repeat ... until expression
The expression is evaluated each time after the loop is executed. This means that the commands inside the loop are executed at least once.
This kind of loop syntax is not usual in BASIC dialects but can be found in languages like PASCAL. Implementing this loop in ScriptBasic helps those programmers, who have PASCAL experience.