10.1.6 Nesting Modifiers
  If you append more than one modifier to a statement, you are
  nesting modifiers . BASIC evaluates nested modifiers from
  right to left. If the test of the rightmost modifier fails, control
  passes to the next statement, not to the preceding modifier on
  the same line.

  In the following example, BASIC first tests the rightmost
  modifier of the first PRINT statement. Because this condition
  is false, BASIC executes the following PRINT statement and
  tests the rightmost modifier. Because this condition is met,
  BASIC tests the leftmost modifier of the same PRINT state-
  ment. This condition, however, is not met. Therefore, BASIC
  executes the following PRINT statement. Because both con-
  ditions are met in the third PRINT statement, BASIC prints
  the value of C .
  A = 5
  B = 10
  C = 15
  PRINT "A =";A IF A = 5 UNLESS C = 15
  PRINT "B =";B UNLESS C = 15 IF B = 10
  PRINT "C =";C IF B = 10 UNLESS C = 5
  END

  Output
  C = 15