Usage not only Number as a layer x/y argument

[AndreiKingsley]

At the moment, if I want to make a constant x in some layer, that value has to be Number. Why can't I use String or datetime type?

[alshan]

Constants accept values of a type matching the type of correspondent aesthetic.
In case of positional aesthetics this is number.

If you want to use a value belonging to your data domain, you can try to use it in mapping:
geom_abc() { x=["my value"]}