non-mandatory attribute; optional attribute
Computing term for an attribute that is not required; often used in contexts like XML, HTML, or data modeling.
You can add optional attributes to this element.
任意選択属性は省略しても構いません。
Non-mandatory attributes may be omitted.
Compound of 任意 (optional), 選択 (selection), and 属性 (attribute). A technical term likely coined in computing contexts.