Zope Page Templates

Zope Page Templates are a web page generation tool. They help programmers and designers collaborate in producing dynamic web pages for Zope web applications. Designers can use them to maintain pages without having to abandon their tools, while preserving the work required to embed those pages in an application.

The goal of Page Templates is to allow designers and programmers to work together easily. A designer can use a WYSIWYG HTML editor to create a template, then a programmer can edit it to make it part of an application. If required, the designer can load the template back into his editor and make further changes to its structure and appearance. By taking reasonable steps to preserve the changes made by the programmer, the designer will not disrupt the application.

Page Templates aim at this goal by adopting three principles:

  1. Play nicely with editing tools.
  2. What you see is very similar to what you get.
  3. Keep code out of templates, except for structural logic.

A Page Template is like a model of the pages that it will generate. In particular, it is a valid HTML page.

How Zope Page Templates Work

Page Templates use the Template Attribute Language (TAL). TAL consists of special tag attributes. For example, a dynamic page title might look like this:

<title tal:content="here/title">Page Title</title>

The tal:content attribute is a TAL statement. Since it has an XML namespace (the tal: part) most editing tools will not complain that they don't understand it, and will not remove it. It will not change the structure or appearance of the template when loaded into a WYSIWYG editor or a web browser. The name content indicates that it will set the text contained by the title tag, and the value "here/title" is an expression providing the text to insert into the tag.

All TAL statements consist of tag attributes whose name starts with tal: and all TAL statements have values associated with them. The value of a TAL statement is shown inside quotes.

To the HTML designer using a WYSIWYG tool, the dynamic title example is perfectly valid HTML, and shows up in their editor looking like a title should look like. In other words, Page Templates play nicely with editing tools.

This example also demonstrates the principle that "What you see is very similar to what you get". When you view the template in an editor, the title text will act as a placeholder for the dynamic title text. The template provides an example of how generated documents will look.
When this template is saved in Zope and viewed by a user, Zope turns the dummy content into dynamic content, replacing "Page Title" with whatever "here/title" resolves to. In this case, "here/title" resolves to the title of the object to which the template is applied. This substitution is done dynamically, when the template is viewed.

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