[ZDP] BackTalk to Document The Zope Book (2.6 Edition)/Using Zope Page Templates

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A comment to the paragraph below was recently added via http://zope.org/Documentation/Books/ZopeBook/2_6Edition/ZPT.stx#2-23

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    The expression, "template/title" in your simple Page Template is a
    *path expression*.  This the most common type of expression. There
    are several other types of expressions defined by the TAL
    Expression Syntax (TALES) specification. For more information on
    TALES see the "Zope Page Templates Reference
    Appendix":AppendixC.stx.

      % Anonymous User - Nov. 4, 2003 9:44 am:
       The Page Templates Reference is only comprehensibe to readers who already understand the language.

       Items like the following are meaningless without some explanation:
            1.:
            argument             ::= attribute_statement [';'                attribute_statement]*
            attribute_statement  ::= attribute_name expression
            attribute_name       ::= [namespace-prefix ':'] Name
            namespace-prefix     ::= Name
       This explains nothing, but it does add considerable confusion.
            2.:
            argument ::= expression
       Does this mean the argument must be an expression?  What are the funny double colons about?
            3.:
            argument ::= (['text'] | 'structure') expression
       That is the significance of the ( .... ), of the [ .... ], When do we use ' .... ' and when not? After all,
       both sometimes work.