Every Page Designer component type has aJSON meta definition. That metadata describes the configurable structure exposed to Page Designer, including attributes and, for container/layout components, theregions into which merchants can place other components.
Salesforce documentation states that each page type and component type requires a JSON meta definition file.
For component types, the file describes merchant-configurable attributes and can define regions. Salesforce ' s example of a three-column layout component represents each column as a region in that component ' s metadata.
The JSON file does not itself define the CSS responsive behavior of the rendered component; responsive visual structure belongs to the component ' s rendering/template implementation and associated styling. Nor does the JSON meta definition contain the complete business and rendering logic. Traditional Page Designer component types have a corresponding script implementation that performs rendering, obtains application data when appropriate, and sends content to the template.
The metadata file is therefore declarative: it describes what Page Designer understands about the component and what configuration merchants can manipulate.
Study Guide reference:Application Development - Page Designer component types, JSON meta definitions, region_definitions, component attributes, and Page Designer architecture.