LaTeX3 Concepts

Architecture

object: A high-level document concept, such as heading, list, or float.
template: A mid-level document concept that are specific use cases of objects, such as section, subsection, enumerate, itemize, table, and figure.
instance: A user-level document concept that implements a given template by specifying its parameters.

template library: A collection of templates defined jointly by the programmer and document designer.
document class realization: A collection of instances.
document type specification: … ?
UI representation: Any single mark-up manifestation of the document type specification.
document: The end product.

author: Responsible for authoring the document. Uses the UI representation designed by the document type designer.
document type designer: Responsible for the high-level logical components of the document. Defines object types with \DeclareObjectType (for the document designer) and creates the document type specification.
document designer: Responsible for the details of the document’s visual manifestation and user interface. Defines the document class realization using a list of declared data types (written by the document type designer), declaring templates with \DeclareTemplateInterface and instances and \DeclareInstance (to be used by the author).
programmer: Responsible for the implementation of templates. Writes template implementations for the document designer using expl3 and \DeclareTemplateCode.