Constant is

pub const is: (&'static str, Option<&'static str>, bool);

https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/is

Usage in rsx

let is = "value";

rsx! {
    // Attributes need to be under the element they modify
    div {
        // Attributes are followed by a colon and then the value of the attribute
        is: "value"
    }
    div {
        // Or you can use the shorthand syntax if you have a variable in scope that has the same name as the attribute
        is,
    }
};