If you use <f:number> in forms, you are able to input operators like + or -, but only two of them.
e is an allowed input too, I assume it refers to e as constant in this case?
Though, if you input e, the form complains about you not providing a number.
This is replicable on https://weekly.ci.jenkins.io/design-library/Progress/, if you head over to progressive rendering and find factors of a number.
that is to allow scientific notation I guess.
1e3 = 1000
1e-3 = 0.001
https://coolconversion.com/math/scientific-notation-to-decimal/Convert_1e3_to-number