ifPartsunlessParts

IfPartsunlessParts is a conditional mechanism used in modular templating and content composition to select between two sets of parts depending on whether particular parts are present. It is designed for environments where pages, components, or products are assembled from multiple parts and where availability of those parts determines what should be shown.

In practice, the construct allows authors to express that the ifParts branch should be included when the required parts exist, and the unlessParts branch should be included when they do not. It is commonly found in template engines, component libraries, and configuration systems that manage content assemblies, such as dynamic pages or configurable products. The goal is to provide a clear, mutually exclusive pathway for content assembly and to support graceful fallbacks.

Semantics commonly involve evaluating a parts-related condition and then rendering the corresponding branch. If the condition is true, the content defined in the ifParts branch is used; if false, the content in the unlessParts branch is used. Some implementations support more complex conditions, multiple part lists, or layered fallback logic to handle edge cases and to maintain a coherent user experience.

Syntax is typically expressed as a directive or function that takes three elements: a condition about parts, an ifParts value, and an unlessParts value. For example, a detailed specification may be shown when parts exist, while a concise overview is shown when they do not.

See also: conditional rendering, fallback content, template directives, mutually exclusive branches.