Templates

What are templates?

Templates are a flexible mechanism ewok provides to allow presentation information - the "look and feel" of a site - to be managed separately from the authored content.

Cascading stylesheets (CSS) already provide this to some extent, but ewok takes the principle further by allowing recurring content elements, like headers, footers, and sidebars, to be abstracted as well. They also remove a key limitation of stylesheets - that content authors remember to link to the appropriate stylesheet in their pages.

ewok templates therefore provide three main benefits: they remove the requirement that authors cooperate with site policies (such as using particular stylesheets) or use an appropriate prefabricated static site template; they allow for a clean separation of responsibility between authors who maintain content and site designers who maintain the look-and-feel; and they isolate presentation changes within the template, allowing modifications to be applied instantly site-wide rather than piecemeal file-by-file.

How do templates work?

ewok templates work by providing a framework within which ewok dynamically renders content pages. The provided content is "wrapped" with template components, allowing standard stylesheets and recurring content elements to be automatically added to every page.

Templates consist of three standard components that are applied to the HTML content page as follows:

style component - the style component is inserted at the beginning of <HEAD> section of the HTML content. This allows standard site stylesheets to be included, but document-specific stylesheets to override the site settings if required. The style component can also be used for any other <HEAD> section content - standard <META> tags or customising <TITLE> content are obvious examples. The default style component is named 'style.epl'.
header component - the header component is inserted at the beginning of the <BODY> section of the HTML content, allowing elements like headers and sidebars to be applied to page content. If HTML tables are used for layout, these can be opened in the header component and closed in the footer. The default header component is named 'header.epl'.
footer component - the footer component is inserted at the end of the <BODY> section of the HTML content, allowing footer content to be added to the page, or layout tables to be closed off. The default footer component is named 'footer.epl'.

Components can simply contain static HTML to be inserted as-is into the rendered page, or they can contain embperl (Embedded Perl) statements, allowing dynamic component content (thus the '.epl' suffix). [ See the Embperl Overview in the User Guide for an introduction to embedded perl ].

Note that the ewok file manager restricts listing, creating, and editing of template components to users with 'template' or 'admin' privilege.

Template inheritance

Template components are inherited in an object-oriented fashion (using EmbperlObject). ewok searches for each component beginning from the directory containing the current content page up to the top of the current ewok tree, as well as any supplementary directories that have been nominated for that tree (see ewok.conf for configuration details).

This allows a template to be defined for a whole website, but for individual components to be overridden for subtrees simply by creating a lower-level component in the subtree. For example, to override the sitewide footer within a particular directory you just create a footer.epl there with the local footer content, and ewok uses that instead. Empty components are also valid, so you can turn off footers for an area simply be creating an empty footer.epl.

The recommended approach is to create a 'templates' directory at the top of each site tree and locate the sitewide template components there, overriding further down the tree if required. (Template components can also be placed directory in the root directory of the tree, but if you use multiple templates - see next section - this can server to unduly clutter your root directory)

[ For advanced EmbperlObject users it's worth pointing out that standard Execute inheritance also works for components - you can say "Execute '../footer.epl'" within a lower footer.epl to add to the existing footer, for example. Even more powerfully, of course, you can also do explicit component munging by Executing a parent component into a scalar and then manipulating that output. ]

Named templates

Templates can also be named, allowing multiple templates to be defined for an area, not just the single default template. Named template components are again identified using using simple naming conventions, having the form 'style-<name>.epl', 'header-<name>.epl', and footer-<name>.epl. Thus to create a new 'foo' template it is only necessary to create 'style-foo.epl', 'header-foo.epl', and 'footer-foo.epl'.

In fact, it's only necessary to create any one of these components to create a named template - if ewok does not find a named component it will fall back to using the default one instead. This allows you to derive a named template from the default one simply be overriding a single component.

Named templates can be selected for use (instead of the default template) in three ways (highest precendence first):

Using an explicit template URL argument: adding a t=<name> URL argument to an ewok page will use the given template e.g. templates.html?t=foo
Setting an explicit template in the 'template' item in your ewok user preferences will use that template (for you only) for all ewok pages - useful for testing. (This can also be achieved by using an explicit template URL argument, as above, but using a doubled tt=<name> to force the template to be sticky.)
Setting the template metadata item on a directory will use the named template for all pages below that point in the tree. This is how to effect more permanent template selection for a tree.

Dynamic template selection only works on staging pages, of course - published pages are static and have had the template 'fixed'. When publishing, ewok uses the given named template if one is defined in the directory metadata for the published page, and the default template otherwise. ewok admins can explicitly override the template to use when publishing.

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