unless: Tests a condition

  The 'unless' tag provides a shortcut for testing negative
  conditions. For more complete condition testing use the 'if' tag. 

  Syntax

    'unless' tag syntax::

      <dtml-unless ConditionVariable|expr="ConditionExpression">
      </dtml-unless>

    The 'unless' tag is a block tag. If the condition variable or
    expression evaluates to false, then the contained block is
    executed. Like the 'if' tag, variables that are not present are
    considered false.

  Examples

    Testing a variable::

      <dtml-unless testMode>
        <dtml-call dangerousOperation>
      </dtml-unless>

    The block will be executed if 'testMode' does not exist, or exists
    but is false.

  See Also

    "if tag":dtml-if.stx