Provide end-users with the ability to customize the markup around shortcode-embeded content

[cferdinandi]

This is achieved by adding a textarea in the settings field where users can write their markup, and providing placeholders that get replaced with key pieces of content when the shortcode renders. Examples:

{{username}}
%field.username%

If custom markup is included, you do a find/replace for the placeholders. Otherwise, you render the default markup. You can see this in action in another plugin I manage: WordPress for Web Apps