[interop] Text fragments + MathML

[dginev]

The URL Fragment Text Directives effort defines an algorithm "find a range from a text directive" which is applicable over <math> nodes. I find the following quote to be a great summary:

The basic premise of this algorithm is to walk all searchable text nodes within a block, collecting them into a list. The list is then concatenated into a single string in which we can search, using the node list to determine offsets with a node so we can return a range.

I am opening this issue to discuss if "a block" is a concept that needs to be extended/refined when that algorithm is executed inside a <math> context.

This could be a very useful refinement, as linking to math-rich fragments is often appropriate when discussing scientific materials.

If there is interest, we can open a mirror issue in the WICG/scroll-to-text-fragment repository. I have checked all repositories for related issues - as far as I am aware this question not been discussed before.

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Examples

Successful

Text fragments are available in chromium browsers, where they also match text nodes inside MathML. I will add 3 examples with screenshots.

1. Link to token element, first instance of <mi>ℝ</mi>

   • fragment used is #:~:text=ℝ
   • https://ar5iv.labs.arxiv.org/html/2106.11285#:~:text=%E2%84%9D
   • 

2. Link to a textual fragment inside <mtext>

   • fragment used is #:~:text=Hodge%20Riemann%20property
   • https://ar5iv.labs.arxiv.org/html/2106.11285#:~:text=Hodge%20Riemann%20property
   • 

3. Link to a range, starting at the first <mi>det</mi> determinant, and upto the end of the closing ) for its matrix.

   • fragment used is #:~:text=det,)
   • https://ar5iv.labs.arxiv.org/html/2106.11285#:~:text=det,%29
   • 

Unsuccessful

1. Link to text nodes in adjacent token elements (grandchildren in the same <mrow>), fails.

   • fragment used is #:~:text=𝑑−2
   • https://ar5iv.labs.arxiv.org/html/2106.11285#:~:text=%F0%9D%91%91%E2%88%922
   • A range is hard to construct here as a 3-part directive isn't a valid range (which I mistakenly tried), i.e. text=𝑑,−,2 is not a range.
   • A regular range, such as d,− or d,2 could succeed, but it would not match the desired expression. Example:
     • fragment used is #:~:text=𝑑,2
     • https://ar5iv.labs.arxiv.org/html/2106.11285#:~:text=%F0%9D%91%91,2

2. Link to adjacent HTML text node and adjacent inline math <mi>, fails

   • fragment used is #:~:text=partition of 𝑑
   • https://ar5iv.labs.arxiv.org/html/2106.11285#:~:text=partition%20of%20%F0%9D%91%91
   • using a range instead succeeds, #:~:text=partition of,𝑑
     • https://ar5iv.labs.arxiv.org/html/2106.11285#:~:text=partition%20of%20,%F0%9D%91%91
     •