feat(jats/inline-formula): Support emphasis elements and Inline formulas

[taru-garg-2000]

#3696 landed inline tex-math rendering for JATS as the first step. This continues that work by handling the styling that can sit alongside the formula inside an <inline-formula>.

When we walk an <inline-formula>, we now break it into ordered inline pieces instead of one flat string: the tex-math becomes the formula, and emphasis around it (italic, bold, underline, strike, sub, sup) is kept as styled text. MathML <mml:math> or other alternatives are skipped — as MathML isn't parsed yet, so we rely on the tex-math sibling instead. The pieces go into an inline group so everything still reads as one continuous line.

A couple of examples:

<p>We use <inline-formula><italic>x</italic> <tex-math>$$a^2$$</tex-math></inline-formula> here.</p>

The x stays italic right next to the a^2 formula.

<p>Index <inline-formula>x<sub>i</sub> <tex-math>$$x_i$$</tex-math></inline-formula> shown.</p>

One thing I noticed with things like Superscript or Subscript, there is a space in between the element which carry that super/sub-script and the actual element in the sub/super-script. To explain, when parsing something like

<p><inline-formula>x<sup>2</sup></inline-formula></p>

We would expect to be rendered as x² but it actually renders as x ² (notice the space), it seems this is because how the elements are serialized, but I haven't looked into it that much.

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[ceberam]

One thing I noticed with things like Superscript or Subscript, there is a space in between the element which carry that super/sub-script and the actual element in the sub/super-script.

This is correct and it affects all parsers. Just accept it as the normal behavior for now. There is another PR in docling-core that will fix it.

[ceberam]

Thanks @taru-garg-2000 for your PR. Please, see my comments below.
I was also wondering if you could extend the styling of text beyond the inline formulas, since it is still missing. I guess it would be pretty simple to reuse the static methods you created to add the formatting of text.

[ceberam]

Why did you remove the explicit fallback for tex-math content that is not wrapped in $$...$$?
Real JATS files from publishers frequently emit bare tex-math without $$ delimiters. Those formulas now silently disappear.

[taru-garg-2000]

So I saw that in the previous PR the behaviour diverged for how tex-math is handled in inline-formula and how it is handled in _add_equation with this PR I wanted to reduce the duplication and since _add_equation existed before, I adapted my implementation considering that as the base, will add back the fallback if that is more favourable.

[ceberam]

It's a good point to align the implementation for both cases. Actually the best approach would have been to use a utility function to avoid the risk of divergence (or we could just reuse _extract_tex_math).

Instead of regressing the code above, we should improve _extract_tex_math by adding the fallback. Actually, according to JATS, the formula inside <tex-math> should not be surrounded by $$ or $ symbols.

Also please note that the original code was treating <tex-math> regardless of the container and creating a Docling document item of type DocItemLabel.FORMULA . The issue we want to resolve here is to enable inline formulas through a Docling document inline group. Therefore it is not enough to add a block elif child.tag == "inline-formula" in _walk_linear to capture the container of the inline formula. We should also consider the container of the block-level formula, which is <disp-formula> to distinguish both cases and then be able to reuse the handing of <tex-math>.

It would also help having a real JATS document in the test suite that includes both inline and block-level formulas. Let me know if you need any help here.

[taru-garg-2000]

For the real JATS document I was wondering if the 2nd document from here would be acceptable ? It seems to contain good number of samples of inline-formula, disp-formula and emphasis tags.

[ceberam]

That looks like a nice sample document with all kind of formulas. Unfortunately, I don't see an explicit open license in the document. We should only include CC0 or CC-BY documents.

[taru-garg-2000]

Ahh okay no worries, I will test on it for now, and see how the changes perform, and find another doc for adding hopefully I find one with an open license. Apologies for the delay on this, I hope to rework it within this week.

[taru-garg-2000]

Hi @ceberam , Thanks a lot for the review! Happy to extend it for generalised implementation on formatting tags, I was wondering though if it would be better to keep it as a separate PR ?

[ceberam]

Hi @ceberam , Thanks a lot for the review! Happy to extend it for generalised implementation on formatting tags, I was wondering though if it would be better to keep it as a separate PR ?

Let's do it in this PR since it will help us better design the formatting in a reusable manner.

[taru-garg-2000]

Hi @ceberam, There's some polishing still left I feel, however was looking to get an early review if the approach looks good ?

For tex-math items I tested on a bunch of real JATS files, and they seems to have this whole blob around them

\documentclass[12pt]{minimal} \usepackage{wasysym} \usepackage[substack]{amsmath} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage[mathscr]{eucal} \usepackage{mathrsfs} \DeclareFontFamily{T1}{linotext}{} \DeclareFontShape{T1}{linotext}{m}{n} { <-> linotext }{} \DeclareSymbolFont{linotext}{T1}{linotext}{m}{n} \DeclareSymbolFontAlphabet{\mathLINOTEXT}{linotext} \begin{document} $$ \frac{dA(t)}{dt}={\gamma}_{i,j,B} \left( { \,\substack{ ^{3} \\ {\sum} \\ _{i=1} }\, }I_{i,F,B}(t)+I_{i,M,B}(t) \right) -{\mu}_{A}A(t)-{\delta}A(t), $$ \end{document}

Which kind of corrupts the render of actual formula

\frac{dA(t)}{dt}={\gamma}_{i,j,B} \left( { \,\substack{ ^{3} \\ {\sum} \\ _{i=1} }\, }I_{i,F,B}(t)+I_{i,M,B}(t) \right) -{\mu}_{A}A(t)-{\delta}A(t)

Although it is latex, we don't really render it correctly when the conversion to markdown happens.

[taru-garg-2000]

Polished up the remaining bit, so for the current implementation we check if the text in a tex-math element is surrounded with $$ or $ if so extract the text within them, else just fallback to the text available in the element (this will not work if there is a lot of latex other than the formula like above), happy to find more samples on real documents and test it out against those.