default constructor.

example member function. @return double the value of `_x`.

member function with a trailing return type. @return "`_x`"

an example nullary function. @return `0`

A static routine that returns the origin point. @return The point `(0, 0)`

an example unary overloaded function @param first the first input parameter @return `first`

Default constructor of default definition.

an example static function with `auto` return type @return `0`

an example static function @return `0`

@brief static member function. @return Zero. By which I mean `0`. In the sources, this comment is on multiple lines.

an example static function with trailing return type @return `0`