A Page Template is a Zope object intended to hold presentation and apply it to content. It holds presentation in the form of an XML or HTML document. The application of this presentation to content is controlled by attributes in the document called Template Attributes. The possible attributes constitute the Template Attribute Language (TAL Reference). Most of these attributes’ values contain expressions referring to objects or perform computations. In Page Templates, these expressions are written in the TAL Expression Syntax (TALES Reference).
A separation of user roles is possible because TAL describes dynamic presentation elements and the inclusion of content, while the expressions encapsulate the (sometimes) complex logic of addressing Zope objects and computing values.
Presentation reuse is addressed through METAL Reference, which allow you to define and use chunks of presentations as parametric macros.
A Presentation Designer uses Page Templates, and may need to know TAL, but doesn’t need to know the expression syntax (TALES). TAL is designed to be comprehensible to a non-programmer.