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Macros (METAL)

The Macro Expansion Template Attribute Language (METAL) standard is a facility for HTML/XML macro preprocessing. It can be used in conjunction with or independently of TAL and TALES.

Macros provide a way to define a chunk of presentation in one template, and share it in others, so that changes to the macro are immediately reflected in all of the places that share it. Additionally, macros are always fully expanded, even in a template's source text, so that the template appears very similar to its final rendering.

A single Page Template can accomodate multiple macros.

Namespace

The METAL namespace URI and recommended alias are currently defined as:

xmlns:metal="http://xml.zope.org/namespaces/metal"

Just like the TAL namespace URI, this URI is not attached to a web page; it's just a unique identifier. This identifier must be used in all templates which use METAL.

Statements

METAL defines a number of statements:

  • metal:define-macro Define a macro.
  • metal:use-macro Use a macro.
  • metal:define-slot Define a macro customization point.
  • metal:fill-slot Customize a macro.
  • metal:define-param Define macro parameters.
  • metal:fill-param Fill macro parameters.
  • metal:import Import macro definitions from external file.

Although METAL does not define the syntax of expression non-terminals, leaving that up to the implementation, a canonical expression syntax for use in METAL arguments is described in TALES Specification.

metal:define-macro

Define a macro

Syntax

metal:define-macro syntax:

argument ::= Name

Description

The metal:define-macro statement defines a macro. The macro is named by the statement expression, and is defined as the element and its sub-tree.

Examples

Simple macro definition:

<p metal:define-macro="copyright">
  Copyright 2004, <em>Foobar</em> Inc.
</p>

metal:define-slot

Define a macro customization point

Syntax

metal:define-slot syntax:

argument ::= Name

Description

The metal:define-slot statement defines a macro customization point or slot. When a macro is used, its slots can be replaced, in order to customize the macro. Slot definitions provide default content for the slot. You will get the default slot contents if you decide not to customize the macro when using it.

The metal:define-slot statement must be used inside a metal:define-macro statement.

Slot names must be unique within a macro.

Examples

Simple macro with slot:

<p metal:define-macro="hello">
  Hello <b metal:define-slot="name">World</b>
</p>

This example defines a macro with one slot named name. When you use this macro you can customize the b element by filling the name slot.

metal:fill-slot

Customize a macro

Syntax

metal:fill-slot syntax:

argument ::= Name

Description

The metal:fill-slot statement customizes a macro by replacing a slot in the macro with the statement element (and its content).

The metal:fill-slot statement must be used inside a metal:use-macro statement.

Slot names must be unique within a macro.

If the named slot does not exist within the macro, the slot contents will be silently dropped.

Examples

Given this macro:

<p metal:define-macro="hello">
  Hello <b metal:define-slot="name">World</b>
</p>

You can fill the name slot like so:

<p metal:use-macro='master.macros["hello"]'>
  Hello <b metal:fill-slot="name">Kevin Bacon</b>
</p>

metal:use-macro

Use a macro

Syntax

metal:use-macro syntax:

argument ::= expression

Description

The metal:use-macro statement replaces the statement element with a macro. The statement expression describes a macro definition.

The effect of expanding a macro is to graft a subtree from another document (or from elsewhere in the current document) in place of the statement element, replacing the existing sub-tree. Parts of the original subtree may remain, grafted onto the new subtree, if the macro has slots. See metal:define-slot for more information. If the macro body uses any macros, they are expanded first.

Examples

Basic macro usage:

<p metal:use-macro='other.macros["header"]'>
  header macro from defined in other.html template
</p>

This example refers to the header macro defined in the other template which has been passed as a keyword argument to ITemplateCache's RenderTemplate method. When the macro is expanded, the p element and its contents will be replaced by the macro.

metal:define-param

Define a macro parameter

Syntax

metal:define-param syntax:

argument             ::= attribute_statement [';' attribute_statement]*
attribute_statement  ::= param_type param_name [expression]
param_type           ::= Parameter Type
param_name           ::= Parameter Name

Description

The metal:define-param statement defines macro parameters. When you define a parameter it can be used as a normal local variable in a macro element, and the elements it contains.

The metal:define-param statement must be used inside a metal:define-macro statement.

Parameter names must be unique within a macro.

Examples

Simple macro with two parameters:

<p metal:define-macro="hello"
   metal:define-param='string name; int age'>
  Hello, my name is <b>${name}</b>.
  I'm <b>${age}</b> years old.
</p>

You can declare parameters with default values:

<p metal:define-macro="hello"
   metal:define-param='string name "Roman"; int age 33'>
  Hello, my name is <b>${name}</b>.
  I'm <b>${age}</b> years old.
</p>

metal:fill-param

Fill a macro parameter

Syntax

metal:fill-param syntax:

argument             ::= attribute_statement [';' attribute_statement]*
attribute_statement  ::= param_name expression
param_name           ::= Parameter Name

Description

The metal:fill-param statement fills macro parameters.

The metal:fill-param statement must be used inside a metal:use-macro statement.

If the named parameter does not exist within the macro, the parameter contents will be silently dropped.

Examples

Given this macro:

<p metal:define-macro="hello"
   metal:define-param='string name; int age'>
  Hello, my name is <b>${name}</b>.
  I'm <b>${age}</b> years old.
</p>

You can fill the name and age parameters like so:

<p metal:use-macro='master.macros["hello"]'
   metal:fill-param='name "Roman"; age 33'>
</p>

metal:import

Import macro definitions from external file

Syntax

metal:import syntax:

argument             ::= import_statement [';' import_statement]*
import_statement     ::= (namespace_name ':') path
namespace_name       ::= Namespace name
path                 ::= Path to file

Description

The metal:import statement imports macro defintions from external files. Macros can be imported to specific namespace, defined by namespace argument part. If the namespace is not specified, macros are imported to default namespace.

Examples

Import macros from file Macros.html into default namespace and use imported macro hello:

<p metal:import="Macros.html">
  <p metal:use-macro='macros["hello"]'
     metal:fill-param='name "Roman"; age 33'>
  </p>
</p>

Import macros from file Macros.html into custom namespace mymacros and use imported macro hello:

<p metal:import="mymacros:Macros.html">
  <p metal:use-macro='mymacros.macros["hello"]'
     metal:fill-param='name "Roman"; age 33'>
  </p>
</p>

Import macros from multiple files into one custom namespace:

<p metal:import="mymacros:Macros1.html;mymacros:Macros2.html">
</p>

Import macros from multiple files into multiple custom namespaces:

<p metal:import="mymacros1:Macros1.html;mymacros2:Macros2.html">
</p>