noun
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.
Compound of 文脈 (context) + 上 (on) + の (possessive) + 必す (required) + 要素 (element). The exact derivation is uncertain; it appears to be a technical calque or coined term in computing contexts.