You can assign an article element type, e.g. 'body', to a GNML format. Such format will then be available only for the body article elements, and won't appear in the list of available formats when you attempt to change the format, for example, of a headline article element, pullquote or similar.
The setting is optional.
The purpose of this feature is better organizing of text formatting. Your body text requires different formatting than your headlines. For example, you will never put a byline in the headline, but you will often put it in the body element. Therefore, if would make no sense that the byline style appears as available for the elements different than body.
By default, to new formats you create, no type is assigned. This makes them available in any article element and on master pages.
The best practices
•It is highly recommended to create formats by element type and to assign to them the appropriate element types.
•It is recommended to create at least one default format for every article element, and to keep the format name the same as the name of the article element. For example, create a 'body' format for the 'body' element, the 'head' format for the head element and so on.
•It is recommended to have at least one format unassigned to any type - that format will be available for master pages.
See also
And also
Formats and the range of frame heights