if: Tests Conditions

  The 'if' tags allows you to test conditions and to take different
  actions depending on the conditions. The 'if' tag mirrors Python's
  'if/elif/else' condition testing statements.

  Syntax

    If tag syntax::

      <dtml-if ConditionVariable|expr="ConditionExpression">
	[<dtml-elif ConditionVariable|expr="ConditionExpression">]
	 ...
	[<dtml-else>]
      </dtml-if>

    The 'if' tag is a block tag. The 'if' tag and optional 'elif' tags
    take a condition variable name or a condition expression, but not
    both. If the condition name or expression evaluates to true then
    the 'if' block is executed. True means not zero, an empty string
    or an empty list.  If the condition variable is not found then the
    condition is considered false.

    If the initial condition is false, each 'elif' condition is tested
    in turn. If any 'elif' condition is true, its block is
    executed. Finally the optional 'else' block is executed if none of
    the 'if' and 'elif' conditions were true. Only one block will be
    executed.

  Examples

    Testing for a variable::

      <dtml-if snake>
        The snake variable is true
      </dtml-if>

    Testing for expression conditions::

      <dtml-if expr="num > 5">
        num is greater than five
      <dtml-elif expr="num < 5">
        num is less than five
      <dtml-else>
        num must be five
      </dtml-if>

  See Also

    "Python Tutorial: If Statements":http://www.python.org/doc/current/tut/node6.html#SECTION006100000000000000000