Image plugin docs don't mention that 'sizes' is required with multiple widths

[w0whitaker]

When using the 'eleventyImageTransformPlugin' with multiple widths set, 11ty complains if 'sizes' is not also set in 'defaultAttributes', but this requirement is not mentioned in the docs.

For example:

eleventyConfig.addPlugin(eleventyImageTransformPlugin, {
        extensions: "html",
        formats: ["webp", "jpg"],
        widths: [200, 800],
        defaultAttributes: {
            loading: "lazy",
            decoding: "async",
        },
    });

generates this error: Error: Missing `sizes` attribute on eleventy-img shortcode from:...

If only one width is set, everything is fine. Adding sizes: "auto" to the defaultAttributes block fixes the error.

Happy to write something up if there isn't something I'm missing.

[Snapstromegon]

You're absolutely right, I can't find anything around this in the docs either. We actually have a comment in the code for it: https://github.com/11ty/eleventy-img/blob/792df26a5f26e56aa8823b37f1410fbfa859e628/src/generate-html.js#L85-L88

If you can write something that links either to the spec or MDN too and describes when someone needs to add the sizes attribute, it would be great!