The idea is to build tokens that take a parameter instead of a fixed name and then use them for things as replacing local urls for help texts or links to drupal.org.
Example tokens:
[local:admin/modules] -> will expand to a local url pointing to the module administration page
[documentation:handbook/modules/system] -> will expand to a link to external documentation, which defaults to drupal.org, in this case http://drupal.org/handbook/modules/system
To my surprise we just need to define the token types and it just works adding some minimal logic in hook_tokens(). Though it wouldn't be bad to really support multiple parameters separated by ':' and adding some mapping logic to the token system.
The patch creates these two token types (local, documentation) and uses them for the first few lines of system module help. Also help texts are greatly simplified by this:
// Old help text (note the parameters at the end)
$output .= '<dd>' . t('The System module allows users with the appropriate permissions to enable and disable modules on the <a href="@modules">Modules administration page</a>. Drupal comes with a number of core modules, and each module provides a discrete set of features and may be enabled or disabled depending on the needs of the site. Many additional modules contributed by members of the Drupal community are available for download at the <a href="@drupal-modules">Drupal.org module page</a>.', array('@modules' => url('admin/modules'), '@drupal-modules' => 'http://drupal.org/project/modules')) . '</dd>';
// New help text (not variables are replaced by tokens)
$output .= '<dd>' . t('The System module allows users with the appropriate permissions to enable and disable modules on the <a href="[local:admin/modules]">Modules administration page</a>. Drupal comes with a number of core modules, and each module provides a discrete set of features and may be enabled or disabled depending on the needs of the site. Many additional modules contributed by members of the Drupal community are available for download at the <a href="[documentation:project/modules]">Drupal.org module page</a>.') . '</dd>';
Of course we need to run help text through token replacement.