Because the builtin calendar doesn't have such an option.
Add more taxonomies to your WordPress installation.
Adds more options to control where Sharedaddy is being displayed.
Link to posts and pages within your blog using shortcodes, similar to a wiki or cms. No need to remember full URLs, post ids or slugs with the wysiwyg
Admin UI for creating dynamic post types and taxonomies in WordPress
Add, Edit, Delete & Manage taxonomies for posts, pages, links and custom post types with a few clicks of mouse. Makes adding taxonomies a 100 time
RSS link for this tag.