'class' attribute value in preAttributes and codeAttributes doesn't work

Description

When a user adds a class attribute value to preAttributes or codeAttributes, nothing happens:

eleventyConfig.addPlugin(pluginSyntaxHighlight, {
    preAttributes: {
      class: "hey-this-is-a-custom-class-name",
    },
    codeAttributes: "this-is-also-custom-class-name",
});

Resulting DOM:

I assume this is because <pre> and <code> already have a class name that denotes the language being used (e.g. language-js).

Possible solutions

1. Maybe we can concatenate the new class names to the existing one, taking care not to overwrite the originals
2. …or add the possibility for the user to add a wrapper element over the <pre>, because the scenario (at least in my case) is to add some layout styling to the code block (say, max-width):

eleventyConfig.addPlugin(pluginSyntaxHighlight, {
    wrapper: {
      element: "div",
      attributes: {
         // here be attributes
      }
    },
});

[zachleat]

This was included as an addendum to #50. If you supply a class attribute to preAttributes or codeAttributes it will override the built-in class="language-${language}" class added to <pre> or <code> respectively.

[zachleat]

No but it’s easy enough to add it back in with the provided callback! The language is passed to the callback