noun
contextually optional token
Technical computing term for a token that may be omitted depending on context, such as in parsing or syntax analysis.
この文法では、文脈上の選択字句は省略可能です。
In this grammar, contextually optional tokens can be omitted.
Compound of 文脈上 (contextual) + の + 選択 (selection) + 字句 (token/character phrase). The exact derivation is uncertain; it appears to be a technical term coined in computing contexts.