Paragraph formats must be mapped to DITA block elements that can contain text, not to inline elements or topic containers.
Make sure target elements can contain text
When you map paragraph formats to DITA block elements, you must ensure that the element mapped to is allowed to contain text. For example, in a <task>, do not map to <step>; map to <cmd> or <info>, which fit inside <step>. For list items that can include more than one paragraph, map the paragraph format(s) to <p>, and designate their including list element; see §24.5 Nesting DITA block elements.
§24.4.3.1 Assigning DITA elements to paragraph formats
§24.4.3.2 Omitting element tags for selected paragraph formats
§24.4.3.3 Specifying a default element for unmapped paragraph formats
§24.4.3.4 Omitting invalid tags for default DITA block elements
§24.4.3.5 Overriding element mapping for paragraph formats
§24.4.3.6 Providing aliases for paragraph formats
§24.4.3.7 Mapping paragraph format aliases to different elements
§24.4.3.8 Mapping paragraph format aliases algorithmically
§24.4.3.9 Mapping several paragraphs formats to the same element