W3C 术语 - axis
axis
中文：轴
解释
The axis is an imaginary alignment line upon which a fraction line is centered. Often, operators as well as characters that can stretch, such as parentheses, brackets, braces, summation signs etc., are centered on the axis, and are symmetric with respect to it.（该轴是一条假想的对齐线，分数线以该对齐线为中心。 通常，运算符以及可拉伸的字符（例如圆括号、方括号、大括号、求和符号等）都以轴为中心，并且相对于轴对称。）
来源
来自：Mathematical Markup Language (MathML) Version 2.0 (2001-02-21)