Inline elements in image descriptions are flattened and stripped

[Feuermurmel]

Consider the following document:

![example](/url)

![*example*](/url)

![`example`](/url)

mdformat changes the document to this:

![example](/url)

![example](/url)

![](/url)

In the second case, the formatting is removed. In the third case, the formatted inline element is removed completely. This is surprising to me and the case of removing the inline element seems dangerous to me. I would have expected mdformat to not change this document.

I looked into the CommonMark specification (6.4 Images), which says that an image description can contain inline elements, but that they should be flattened to the plain text content of the elements when rendering to HTML.

This means that in the second case, some information is lost because the document could be rendered to an output format that supports styled image descriptions and in the third case, part of the text is lost.

My setup:

$ pip install mdformat
Collecting mdformat
  Downloading mdformat-0.7.17-py3-none-any.whl.metadata (8.7 kB)
Collecting markdown-it-py<4.0.0,>=1.0.0 (from mdformat)
  Using cached markdown_it_py-3.0.0-py3-none-any.whl.metadata (6.9 kB)
Collecting mdurl~=0.1 (from markdown-it-py<4.0.0,>=1.0.0->mdformat)
  Using cached mdurl-0.1.2-py3-none-any.whl (10.0 kB)
Downloading mdformat-0.7.17-py3-none-any.whl (28 kB)
Using cached markdown_it_py-3.0.0-py3-none-any.whl (87 kB)
Installing collected packages: mdurl, markdown-it-py, mdformat
Successfully installed markdown-it-py-3.0.0 mdformat-0.7.17 mdurl-0.1.2

I ran mdformat without arguments:

mdformat foo.md

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[hukkin]

Thanks for the issue!

The third case seems like a duplicate of #414