How do template-based emails work in Content Builder? What are locked and unlocked regions?

Template-based emails in Content Builder use a template that defines the structural layout — headers, footers, column arrangements. The template defines content slots (also called content areas or editable regions).
Locked regions: Areas defined in the template that child email creators cannot modify. Typically used for brand-mandated headers, footers, and legal disclaimers. Locked via the locking property in the template code.
Unlocked regions: Slots where email creators can drag-and-drop content blocks (images, text, buttons, dynamic blocks). Each slot has a defined content type restriction (e.g., image only, any block).
This structure ensures brand consistency while giving content creators flexibility. Super content blocks can be inserted into templates as globally locked brand elements editable only by admins.