Standard Pascal has a number of rules that are meant to ensure that the control variable of a for statement is modified only by the for statement, and any other statement that can modify the control variable, while the for statement is executing is said to threaten the control variable. In Standard Pascal it is an error to threaten the control variable of a for statement.
When all extensions are disabled (which can be done only with the command-line compiler), Irie Pascal also considers it an error to threaten the control variable of a for statement. When all extensions are not disabled (which is always the case when using the IDE), Irie Pascal does not consider it an error to threaten the control variable of a for statement, instead this warning message is displayed.