Movable Type allows you to enter a list of categories, then assign one or more categories to each of your entries. This allows you to keep track of your entries from a maintenance standpoint--for example, when listing your entries you can choose to list entries only from a particular category--and it can also be used to provide a categorization structure to your archives.
Each entry can be assigned one primary category and any number of secondary
categories. The primary category is used when you wish to display information
about only one of the categories to which an entry is assigned--for example,
when using the <$MTEntryCategory$> tag. When you wish to display
a list of all of the categories to which a post has been assigned, you can use
the <MTEntryCategories> container.
The difference between primary and secondary categories is not one of ranking
but rather of usage--your secondary categories are not necessarily ``lesser''
or ``lacking in importance'' when compared to your primary category. Rather, the
difference is one of usage: the primary category is the category which will
be displayed when using the <$MTEntryCategory$> tag, or when
linking to the Category archive for an entry using
<$MTEntryLink archive_type="Category"$>.
You can manage your list of categories in Movable Type by logging in,
selecting a weblog, then clicking Categories. Add new categories by
typing their labels into the empty text entry boxes; the system always shows
five empty boxes, so if you fill up the first five, just press SAVE and
you'll get five more.
Categories can also have a hierarchical structure. For example, if you have two categories, Books and Music, you could now create a new category, Entertainment, which contains both of the others; we call Entertainment the ``parent'' category of the Books and Music categories.
Categories with no parent are called root-level categories. All categories default to being at the root-level initially when importing from previous versions of Movable Type (unless you used the SubCategories plugin and imported the data from that).
To create a category with a specific parent, click the ``Create'' link in the Actions column in that specific category's row and a text input box will appear, along with a ``Create Category'' button. Just fill in the label for the category and click the button.
To move a category to a different parent, click the ``Move'' link in the Actions column in that specific category's row and then select the radio button next to the new parent category (or ``Root'' if you wish to move the category to the root-level).
By clicking the Edit category attributes link, you can edit some additional metadata regarding the category. You can associate a description with each of your categories. This description can then be used on your archive pages, for example, as introductory text describing that particular category and the entries within it.
You can also manage TrackBack-related information for the category:
After clicking the ``On'' checkbox, save the changes, and the system will give you the TrackBack URL that other users can use to ping your category.
This is a good way to enable ``private'' TrackBack items; even if someone can guess the TrackBack ID, he will not be able to send a ping unless he knows the passphrase.
This is optional. If you do not set a passphrase, everyone will be able to ping you without providing a passphrase.
You can set up category archiving in your weblog configuration--select a weblog, then click Weblog Config. In the Archive Configuration section, under Archive Frequency check the box next to By Category.