From Zimbra :: Wiki

The config_template.xml file specifies a template for Zimlet configuration. There are two sections to this file: a section for global configuration, and a section for per host configuration.

The configuration properties maybe accessed within the Zimlet definition file as follows:

<zimletConfig name=”com_acme_Maps” version=”1.0”>
   <global>
     <property name=”defaultToGoogle”></property>
   </global>
   <host name=””>
     <property name=”googleApi”></property>
     <property name=”geocodeUser”></property>
     <property name=”geocodePass”></property>
   </host>
</zimletConfig> 

The properties defined in config_template.xml may be accessed within the Zimlet definition file as follows:

• ${config.global.propertyName} - Accesses a global property. For example, the global property defaultToGoogle

would be accessed as: ${config.global.defaultToGoogle}

• ${config.host.propertyName} - Access a host specific property. For example, the host property googleApi would be accessed by ${config.host.googleApi}

Configuration properties are also available to Zimlet JavaScript code via Zimlet classes method getConfigProperty.