subforms

A subform is a form embedded within a parent form to collect related data. It represents a separate subset of fields that belongs to a related record or structured component, and is presented as a section of the main form. Subforms are commonly used to model one-to-many or hierarchical data within a single user interface.

Subforms can be static (a fixed number of instances) or dynamic (the user can add or remove instances at runtime). When the parent form is saved, the state of the subforms is typically preserved and translated into the corresponding child records in the data model. Validation usually occurs at the subform level, with errors associated to the specific instance; in many implementations, errors may bubble up to the parent.

Common use cases include a profile form with multiple addresses, a product entry form with several variants, or an order form containing multiple line items. In administrative interfaces, subforms are often realized as inline formsets or nested editors that let users manage related data from a single page.

Design and technical considerations include ensuring a clear and accessible layout, managing the naming and state of repeated fields, handling data binding to nested data structures, and addressing performance and validation complexity. Not all form frameworks support nested subforms, and implementing them may require custom logic for persistence and error reporting.