contextually required element
Computing term for an element that must be present based on surrounding context, such as in markup or configuration files.
XMLでは、文脈上の必す要素が欠けているとパースエラーになる。
In XML, if a contextually required element is missing, a parsing error occurs.
A technical phrase comprising 文脈上 “in context,” の, and 必須要素 “required element”; the spelling 必す represents 必須 with its second element written in kana.