Rubyで使われる記号の意味(正規表現の複雑な記号は除く) (Ruby 3.4 リファレンスマニュアル)
[[ref:ex]] [[ref:q]] [[ref:num]] [[ref:per]] [[ref:and]] [[ref:or]]
[[ref:plus]] [[ref:minus]] [[ref:ast]] [[ref:slash]] [[ref:hat]] [[ref:sq]]
[[ref:period]] [[ref:comma]] [[ref:langl]] [[ref:rangl]] [[ref:eq]] [[ref:tilde]]
[[ref:dollar]] [[ref:at]] [[ref:under]] [[ref:lbra]][[ref:rbra]]
[[ref:lbra2]][[ref:rbra2]] [[ref:lbra3]][[ref:rbra3]] [[ref:dq]] [[ref:colon]] [[ref:ac]]
[[ref:backslash]] [[ref:semicolon]]
https://docs.ruby-lang.org/ja/latest/doc/symref.html