Limiting is a syntactic way to set boundaries for variables. The way FOL does is by using [] right after the type declaration type[], so: type[options][limits]
Initger limiting
Example, making a intiger variable have only numbers from 0 to 255 that represents an RGB value for a single color:
var rgb: int[][.range(255)];
Character limiting
It works with strings too, say we want a string that can should be of a particular form, for example an email:
var email: str[][.regex('[._a-z0-9]+@[a-z.]+')]