Interestingly, [w3.org Math Double struck] shows example glyph rendering with swapped double stroke stem ("//" + "\" instead of "\\" + "/"). Been looking what

Interestingly, [w3.org Math Double struck] shows example glyph rendering with swapped double stroke stem ("//" + "\" instead of "\\" + "/"). Been looking what the "opf" in the `𝕏` HTML entity name of this kind of character means, and apparently it is "Open Face". It is referenced at [wikipedia Blackboard bold] that mentions that "𝕏 Occasionally used to denote an arbitrary metric space. " [w3.org Math Double struck]: https://www.w3.org/Math/characters/double-struck.html https://www.w3.org/Math/characters/double-struck.html [wikipedia Blackboard bold]: https://en.wikipedia.org/wiki/Blackboard_bold https://en.wikipedia.org/wiki/Blackboard_bold