The Template Attribute Language (TAL) standard is an attribute language used to create dynamic templates. It allows elements of a document to be replaced, repeated, or omitted.
The statements of TAL are XML attributes from the TAL namespace. These attributes can be applied to an XML or HTML document in order to make it act as a template.
A TAL statement has a name (the attribute name) and a body (the
attribute value). For example, an
content statement might look
tal:content="string:Hello". The element on which a statement
is defined is its statement element. Most TAL statements
require expressions, but the syntax and semantics of these
expressions are not part of TAL. TALES is recommended for this
The TAL namespace URI and recommended alias are currently defined as:
This is not a URL, but merely a unique identifier. Do not expect a browser to resolve it successfully.
Zope does not require an XML namespace declaration when creating
templates with a content-type of
text/html. However, it does
require an XML namespace declaration for all other content-types.
These are the tal statements:
Expressions used in statements may return values of any type, although most statements will only accept strings, or will convert values into a string representation. The expression language must define a value named nothing that is not a string. In particular, this value is useful for deleting elements or attributes.
When there is only one TAL statement per element, the order in which they are executed is simple. Starting with the root element, each element's statements are executed, then each of its child elements is visited, in order, to do the same.
Any combination of statements may appear on the same elements,
except that the
replace statements may not appear
When an element has multiple statements, they are executed in this order:
on-error statement is only invoked when an error occurs,
it does not appear in the list.
The reasoning behind this ordering goes like this: You often want
to set up variables for use in other statements, so
first. The very next thing to do is decide whether this element
will be included at all, so
condition is next; since the
condition may depend on variables you just set, it comes after
define. It is valuable be able to replace various parts of an
element with different values on each iteration of a repeat, so
repeat is next. It makes no sense to replace attributes and
then throw them away, so
attributes is last. The remaining
statements clash, because they each replace or edit the statement