Form field rendering objects and form-field conditions/validators.
Form fields control how inputs render inside forms. Typed field objects are on Form Field. Each field has exactly one polymorphic show/hide {{ condition }} (see Form Field Conditions). Some field types also expose a {{ validators }} object with a flat list of polymorphic {{ validator }} items; other field types do not (see Form Field Validators). Liquid {% if %} operators remain under Conditions Overview.
How a form field is declared - its Type, its Condition, and its Validators - is catalogued under Custom Fields. The pages here cover the Liquid objects a form template reads.