anchor.diff:  
   (def-attribute-handler tal::when (tag)
     (let ((value (read-tal-expression-from-string
  -		(pull-attrib-val tag 'tal::when))))
  +		(pull-attrib-val! tag 'tal::when))))
       `(when ,value
          ,(transform-lxml-form tag))))
   
   (def-attribute-handler tal::unless (tag)
     (let ((value (read-tal-expression-from-string
  -		(pull-attrib-val tag 'tal::unless))))
  +		(pull-attrib-val! tag 'tal::unless))))
       `(unless ,value
          ,(transform-lxml-form tag))))
   
  
positive.code:   ;; </tal>
    (let ((template-name
  	 (or
  	  (pull-attrib-val tag 'tal::name)
  	  (awhen (pull-attrib-val tag 'tal::name-expression)
  	    (parse-tal-attribute-value it))
  	  (error "Missing TAL:NAME and TAL:NAME-EXPRESSION tags."))))
  
  
negative.code:   (let ((bindings
           (loop
              for (name value) in (read-tal-expression-from-string
  				 (pull-attrib-val! tag 'tal::let))
              collect `(cons ',name ,value))))
      `(let ((-tal-environment- (extend-environment (list (list ,@bindings)) -tal-environment-)))
         ,(transform-lxml-form tag))))
  