Subforms are a key building block of the ARK interface. Subforms are short php scripts that may have been written by either the core ARK team or as plugins. Please take care to read the inline documentation for each form.
Subforms are configured on a 'use by use' basis by means of php arrays which are normally held in the mod_settings files. Each subform contains information about how it should display itself under default circumstances. It is highly likely that the same subform script may be used many times over within a given configuration but with different set up. Therefore each use of the subform requires a new config array.
Subforms may contain one or many fields and may contain mixed field types. Some subforms are more generic than others. sf_txt for instance is a very generic and multiuse subform whilst other subforms have a single very specific purpose and may require their own configuration options.