Fails when numbers are provided in class names

[mitchhentges]

Bootstrap's grid system involves classes with numbers, such as col-sm-2. This fails at compilation with the error: "expected string".

For example:

html! {
    .col-sm-2 {}
}

error: expected string
 --> file.rs:6:34
  |
n |     let markup = html! { .col-sm-2 {} };
  |                                  ^

[lambda-fairy]

Does this work?

html! {
    ."col-sm-2" {}
}

The confusing error message is covered by #208, but I just notice that the docs don't mention this at all... whoops 🤦