Enhance rule MD033 to be more specific

[mvilrokx]

Describe the Enhancement:

I want to be able to narrow the scope of allowable HTML tags beyond just the tag name.

Impacted Rules:

MD033

Describe the Need:

I want to use rule MD033/no-inline-html, but there are genuine reasons to use some HTML Tags over plain markdown in certain cases. E.g. I only want to allow the usage of the <img> tag if that tag has a style, width or height attribute. Or, to put it another way: I do not want to allow the usage of the <img> tag if it only has attributes src and/or alt.

The reason behind this is that an <img> tag that has just a src or alt attribute can be perfectly described in plain Markdown:

<img src="./picture.png" alt="a picture" />

becomes

![a picture](./picture.png)

If it has any other attribute, it cannot be converted to a Markdown tag without affecting the way it gets rendered:

<img src="./picture.png" alt="a picture" height="100px" width="100px" />

<img src="./picture.png" alt="a picture" style="display: block; margin-left: auto; margin-right: auto; float: none; />

And therefor I would consider this acceptable usage of the <img> tag.

The problem is that the rule only allows exceptions at the "tag" level, e.g. "allowed_elements": ["img"]. I want to be able to narrow the scope by adding exceptions to this.

Current Alternative

Set "allowed_elements": ["img"], but this will allow all <img> tags whereas I only want to allow some.

Can We Help You Implement This?:

Yes, but I'd first like to get some input if this is deemed useful.

If it is, we need to discuss how this would be configured. Some examples:

Original:

{
  "MD033": {
    "allowed_elements": [
      "img"
    ]
  }
}

Enhancement:

{
  "MD033": {
    "allowed_elements": [{
        "img": {
          "except_if_it_contains_only_these_attributes": ["src", "alt"]
        }
    }]
  }
}

(sorry about the name, suggestions are welcome :-))

This would allow the <img> tag, except if it contains only src or only alt or only both

Alternative Enhancement:

{
  "MD033": {
    "allowed_elements": [{
        "img": {
          "allowed_attributes": ["style", "width", "height"]
        }
    }]
  }
}

This would allow the <img> tag, but only if it contains any of "style", "width" or "height" (or any combination).

To be honest I am not sure how useful the later suggestion is since there are many other attributes that could be used on <img> tags that are not convertible to plain markdown, e.g. title, and I would want to exclude those to but then the list in allowed_attributes would have to contain all attributes except src and alt.