This is a simple reference guide to the TAL and TALES languages. Formal language specifications are hosted by Zope online. Axiom TAL differs slightly in the noted areas.

TAL Commands

TAL consists of eight different commands. There is a clear order of operations by which they will be evaluated. Commands are attributes on HTML or XML tags.

Example:<div tal:content="article">Article goes here</div>

The order of operations is as follows:

define
condition
repeat
repeat-children
content
replace
attributes
omit-tag

tal:define

tal:define="[local | axdevdoc:global] name expression [axdevdoc:; define-expression...]

Sets the value of "name" to "expression". By default the name will be applicable in the "local" scope, which consists of this tag, and all other tags nested inside this tag. If the "global" keyword is used then this name will keep its value for the rest of the document.

Example:<div tal:define="global title book/theTitle; local chapterTitle book/chapter/theTitle">

tal:condition

tal:condition="expression"

If the expression evaluates to true then this tag and all its children will be output. If the expression evaluates to false then this tag and all its children will not be included in the output.

Example:<h1 tal:condition="user/firstLogin">Welcome to this page!</h1>

tal:repeat

tal:repeat="name expression"

Evaluates "expression", and if it is a sequence, repeats this tag and all children once for each item in the sequence. The "name" will be set to the value of the item in the current iteration, and is also the name of the repeat variable. The repeat variable is accessible using the TAL path: repeat/name and has the following properties:

index - Iteration number starting from zero
number - Iteration number starting from one
even - True if this is an even iteration
odd - True if this is an odd iteration
start - True if this is the first item in the sequence
end - True if this is the last item in the sequence. For iterators this is never true
length - The length of the sequence. For iterators this is maxint as the length of an iterator is unknown
letter - The lower case letter for this iteration, starting at "a"
Letter - Upper case version of letter
roman - Iteration number in Roman numerals, starting at i
Roman - Upper case version of roman

Example:
<table>
<tr tal:repeat="fruit basket">
<td tal:content="repeat/fruit/number"></td>
<td tal:content="fruit/name"></td>
</tr>
</table>

tal:repeat-children

tal:repeat-children="name expression"

Behaves identically to tal:repeat, except that only the child nodes are repeated.

tal:content

tal:content="expression"

Replaces the contents of the tag with the value of "expression". Axiom differs from Zope TAL in that there is no need for the "structure" prefix. DOM Documents and DocumentFragments are imported as nodes, and all other types are converted into strings and quoted for XML representation.

tal:attributes

tal:attributes="name expression[axdevdoc:;attributes-expression]"

Evaluates each "expression" and replaces the tag's attribute "name". If the expression evaluates to nothing then the attribute is removed from the tag. If the "expression" requires a semi-colon then it must be escaped by using ";;".

Example:<a tal:attributes="href user/homepage;title user/fullname">Your Homepage</a>

Note: If you use a javascript reserved keyword for the name, you must enclose it in quotes. E.g.:

Example:<div tal:attributes="'class' user/homepage;id user/fullname">Your Homepage</a>

tal:omit-tag

tal:omit-tag="expression"

Removes the tag (leaving the tags content) if the expression evaluates to true. If expression is empty then it is taken as true.

Example:<p><b tal:omit-tag="not:user/firstVisit">Welcome</b> to this page!</h1>

tal:text

tal:text="escape-character"

Replaces all strings matching escape-character{javascript-expression} in the top-level text nodes beneath this element.

Example:<div tal:text="$">Logged in as: ${session.user.username}</div>

TALES Expressions

The expressions used in TAL are called TALES expressions. The simplest TALES expression is a path which references a value, e.g. page/body references the body property of the page object.

path

[path:]string[| axdevdoc:Expression]

A path, optionally starting with the modifier 'path:', references a property of an object. The '/' delimiter is used to end the name of an object and the start of the property name. Properties themselves may be objects that in turn have properties. The '|' ("or") character is used to find an alternative value to a path if the first path evaluates to null or does not exist.

Example:<p tal:content="book/chapter/title | string:Untitled"></p>

There are several built in paths that can be used in paths:

repeat - access the current repeat variable (see tal:repeat)
attrs - a dictionary of original attributes of the current tag

exists

exists:path

Returns true if the path exists, false otherwise. This is particularly useful for removing tags from output when the tags will have no content.

Example:<p tal:omit-tag="not:exists:book/chapter/title" tal:content="book/chapter/title"></p>

References

Zope documentation on the [TAL directives].

not

not:tales-path

Returns the inverse of the tales-path. If the path returns true, not:path will return false.

Example:<p tal:condition="not: user/firstLogin">Welcome to the site!</p>

string

string:text

Evaluates to a literal string with value text while substituting variables with the form ${pathName} and $pathName

Example:<b tal:content="string:Welcome ${user/name}!"></b>

Axiom TAL - Axiom

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