[Zope-CMF] <metal> and <tal> tag in ZPT

[Michael McLay]

In the page template portal_skins/zpt_generic/main_template the following 
statement seems to be an error. 

    <metal:block define-slot="base" /> 

I found no reference to a <metal> in the current METAL or TAL specification.

I also found serveral comments in the Zope Book AdvZPT in which a <tal> tag 
was used. Here's one of the examples:

  <tal:formfields repeat="field python:form.get_fields()">
  <tal:fieldid define="fieldId python:field.getId()">
  <tal:m_formaterrorbyfield
        metal:use-macro="here/PT_macros/macros/formatErrorByField"
        condition="python:errorMap.has_key(fieldId)">
  <p class="errorMessage"
               tal:content="python:errorMap[fieldId].error_text"></p>
  </tal:m_formaterrorbyfield>
  </tal:fieldid>
  </tal:formfields>

Is this residual syntax from an earlier form of TAL and METAL?  This seems to 
be the case but the <tal> comments were posted very recently. Is the syntax 
a new addition to TAL?

Muddling through the documentation for over an hour has not made the correct 
interpretation apparent to me. Am I missing something obvious?