Template Attribute Language

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The Template Attribute Language ( TAL , roughly translated: “Attribute-based template language”) is a template language for generating HTML and XML (and thus also XHTML ) pages. Its aim is to facilitate the collaboration between designers and programmers by making both the templates and the results pages valid documents in their markup language . The templates can therefore be edited with design tools that don't know anything about TAL, but leave unmolested attributes unmolested.

The TAL was created within the framework of the Zope web application server ; they usually speak of Zope Page Templates .

TAL completely abstracts from the programming language used; only the language used for expression evaluation (usually TALES ) can allow language-specific expressions depending on the implementation, mostly in Python .

overview

TAL templates are created as result documents in which the variable content is overridden by special attributes; Program code outside of elements such as B. in PHP or JSP is not necessary. In the following example, the element <h1> 

<h1 tal:content="string:Eine völlig andere Überschrift">
   Für den Designer sichtbare Überschrift
</h1>

from a common HTML editor as 

<h1>
   Für den Designer sichtbare Überschrift
</h1>

handled while the application of the template by the application server 

<h1>
   Eine völlig andere Überschrift
</h1>

results. Specifying a constant string is of course a rather negligible case in practice; the possible attribute values ​​are defined by the TAL Expression Syntax ( TALES ). For example, Python expressions can be used in the existing Python implementations .

If XML documents are to be generated, it is important to enter the XML namespace ( xmlns:tal="http://xml.zope.org/namespaces/tal").

Macros

With the help of METAL (Macro Expansion TAL) it is possible to reuse code across template boundaries.

internationalization

With the help of the i18nattributes (see i18n TAL ) localized pages can be generated.

Attributes

The following attributes are recognized, which normally tal:have to be preceded by the prefix :

define
creates valid, local variables within the block defined by the element
condition
decides whether the element is created
repeat
creates a loop variable that is used to iterate over a sequence, e.g. B. to create a selection list or a table
content
replaces the content of the element
replace
replaces the element (and therefore cannot be used together with content or attributes)
attributes
replaces the specified attributes (e.g. the tal:attributes="name name; id name"name and ID attribute of an input field could be defined using the variable "name")
omit-day
allows the tag to be omitted dynamically and only the content to be displayed
on-error
will be executed if an error occurs and then works like "content"

If an element has several TAL attributes, these are evaluated (regardless of the order in which they are listed) in the order given above (logically obvious); the order of the variable definitions within a "define" attribute is significant, however, so that a variable can be used in the same define attribute in later assignments.

If there is no element that can be used to carry the TAL attributes, special TAL tags can also be used; in this case the prefix is tal:optional. Example: 

<tal:if condition="context/itemlist">
   ...
</tal:if>

The code within the <tal:if>element is used if, for example, the variable “itemlist” defined in the context (whatever that means for the application server used, for example an object) is true , i.e. contains at least one element in the case of a list. The identifier after the colon is arbitrary; it just has to be the same for the opening and closing day.

use

TAL / TALES / METAL are used by the following projects:

Other implementations

In addition to the original Zope implementation, there are (without claiming to be exhaustive) the following:

Java

JavaScript

Pearl

PHP

python

XSL

See also

literature

  • Erik Möller: Template TALent - web templates with TAL, TALES and METAL (practice, TAL templates for Zope X3, Template Attribute Language, TAL, TALES, METAL, content management system, CMS, PHPTAL, PETAL, JavaZPT) . In: c't , 3/2005, p. 194

Web links