A conditional assembly block is a series of source statements that are assembled only if a certain condition is met. A .IF starts the conditional block and a .ENDC ends the conditional block; each .IF must have a corresponding .ENDC. The .IF directive contains a condition test and one or two arguments. The condition test specified is applied to the arguments. If the test is met, all MACRO-64 statements between .IF and .ENDC are assembled. If the test is not met, the statements are not assembled. Optionally, you can use the .ELSE directive (or a combination of the .IFF, .IFT, and .IFTF directives) to specify an alternate series of statements to assemble if the test is not met. You can nest conditional blocks; that is, a conditional block can be inside another conditional block. In this case, the statements in the inner conditional block are assembled only if the condition is met for both the outer and inner block.