Using Preview-Design Editor for Dynamic Content
The Campaign Designer provides a convenient way to create, edit, and/or preview HTML and plain-text content for your campaign messages, forms, and dynamic content. Learn more about the Campaign Designer.
The Design tab is where you associate content regions with dynamic content modules or define their contents and the rules that will determine what each recipient or submitter sees.
Before you establish that association, the region looks like 
Content Rules Needed; once the association is made, the region looks like Name. Content regions created with SPAN or DIV tags may also include a hint or other information.
(See Editing Message and Form Content for edit details.)
A content region is simply a location for a dynamic content module. Rather than naming the region, you are actually associating it with a dynamic content module, whether the module already exists or you define it on the fly. Move the pointer over the region to see the space it occupies, and click on the highlighted region to define, view, or change its dynamic content. You can also choose whether to include the defined module in the Dynamic Content Report.
Defining Dynamic Content
Set up the rules that will control what content appears at this location in the delivered message. Add rules, and use 
and 
to rearrange them so they'll be evaluated, top to bottom, in the order you want.
For each content region, you can select an existing dynamic content module or template, or define a new one by naming it and setting up a series of rules to insert plain text (which can include Connect API functions and any other text that is appropriate for the format you're editing), a document you select from a folder in your account, or nothing (example: as a default rule).
Note: Same list contains an option to delete the region from the document in the selected format.
Once you've specified the content to be inserted by this dynamic content module in one format, you can copy it and paste that content into the other formats for the same module, within the context of the blue edit pane (without having to select a new document type in the upper left corner). This makes it easier to ensure that the same dynamic content will be displayed in all formats of your campaign message within the capabilities of each format.
Important: Be sure to click Save before closing the window. Otherwise, your unsaved changes will be discarded.