Overrides without JavaScript

3. Overrides without JavaScript#

Many customizations don’t need a single line of JavaScript. In this chapter, we make external links open in a new window, site-wide, with pure XML.

3.1. How pattern options travel#

The registry record plone.patternoptions is a dictionary that maps a pattern name to a JSON string of options. Plone renders each entry as a data-pat-<name> attribute on the <body> element. The pattern’s options parser walks up the DOM tree, so every pattern element inherits these options.

Plone itself uses this mechanism, and configures pickadate and plone-modal this way.

3.2. Exercise: change options through the web#

Open Site Setup ‣ Management ‣ Configuration Registry and search for plone.patternoptions. Add an entry with the key markspeciallinks and the value:

{ "external_links_open_new_window": "true" }

Reload the page, and inspect the <body> element in the developer tools. Notice the new data-pat-markspeciallinks attribute. External links in the content area now open in a new window.

3.3. Persist it in a GenericSetup profile#

A through-the-web change lives in the database only. We persist it in the add-on’s profile instead, in profiles/default/registry/patternoptions.xml:

<?xml version="1.0" encoding="utf-8"?>
<registry>
  <record name="plone.patternoptions">
    <value purge="false">
      <element key="markspeciallinks">{"external_links_open_new_window": "true"}</element>
    </value>
  </record>
</registry>

Important

Keep purge="false". Without it, the import wipes the entries of the Plone core and of other add-ons.

3.4. The trigger class catch#

Options alone don’t run a pattern. The trigger class must be present in the DOM.

The pat-markspeciallinks class on the <body> is only rendered when one of Plone’s link settings is enabled. That’s why the profile also enables plone.mark_special_links in profiles/default/registry/linksettings.xml:

<?xml version="1.0" encoding="utf-8"?>
<registry>
  <record name="plone.mark_special_links">
    <value>True</value>
  </record>
</registry>

When a pattern “does nothing”, first check the trigger, then the options.

3.5. Precedence#

An entry in plone.patternoptions overrides the <body> attribute that Plone’s IPatternsSettings adapters render for the same pattern. This includes the link settings from the control panel. This is powerful, so be deliberate.

3.6. Checkpoint#

External links open in a new tab, and you did not run any build.

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