noun
name start character
Computing term for the first character of a name, used in contexts such as XML, programming languages, or data validation.
XMLでは、名前開始文字として使える文字が決まっている。
In XML, the characters that can be used as a name start character are defined.
Compound of 名前 (name) + 開始 (start) + 文字 (character). A technical term likely calqued from English 'name start character'.