tagging produces an extra line above align environment if text line above is completely full (pdftex only)

[John02139]

The following occurs with pdftex, not lualatex, and requires that the text line above the display is completely full. (Removing one character stops an apparent overflow.)

\DocumentMetadata{
	testphase = {phase-III,math,table,title,firstaid},
	pdfstandard=ua-2,
	pdfversion=2.0,
	lang=en-US,
}
\documentclass{article}
\usepackage{amsmath}


\begin{document}

% the last line before align must be completely full.
Cras nec ante. Pellentesque a nulla. Cum sociis natoque penatibus et
magnis dis parturient montes, nascetur ridiculus mus. Aliquam tincidunt urna.
Nulla ullamcorper vestibulum turpis. Pellentesque cursus luctus mauris. Pellentesque:
\begin{align}
\frac{d\Gamma}{dt} &= \frac{d}{dt} \int_{\mathcal{C}} \mathbf{u} \cdot d\mathbf{r}\\
				   &= \int_{\mathcal{C}} \frac{D\mathbf{u}}{Dt} \cdot d\mathbf{r} + \underbrace{\int_{\mathcal{C}} \mathbf{u}\cdot d\biggl( \frac{d\mathbf{r}}{dt}\biggr)}_{=\, 0} \\[-2pt]
                   &= \iint_{\mathcal{S}} \nabla \times \frac{D\mathbf{u}}{Dt}  \cdot d\mathbf{A}\\
                   &= \iint_{\mathcal{S}}  \nabla p \times \nabla \left( \frac{1}{\rho}\right) \cdot d\mathbf{A}
\end{align}

\end{document}

With tagging, an extra blank line above the equations:

Without tagging:

[u-fischer]

I think there is an \unskip missing, see below (alternatively hide the end of line with a percent char).

Beside this: please be aware that your code does not give an PDF/UA-2 conformant document automatically. PDF/UA-2 explicitly requires that mathematic expression should use MathML:

Mathematical expressions shall be represented using either structure types defined in presentation MathML, as specified in ISO 32000-2:2020, 14.8.6.3, or as presentation MathML via the Associated Files mechanism specified in ISO 32000-2:2020, 14.13.6, or both.

To fulfil the requirement you need to provide a MathML-version of the equation that can then be included as associated file (the latex-lab-math documentation contains instructions for this). Without such a MathML you should not claim conformance with UA-2.

If you want a MathML representation automatically you have to use lualatex + unicode-math.

\DocumentMetadata{
	testphase = {latest},
	pdfstandard=ua-2,
	pdfversion=2.0,
	lang=en-US,
}
\documentclass{article}
\usepackage{amsmath}
\ExplSyntaxOn
\cs_set_protected:Npn \__tag_tool_close_P:
  {
    \tag_if_active:T
     { \unskip %<-------------
       \tag_mc_end: %end P-chunk, should perhaps be \tag_mc_end_push: ...
         \__tag_gincr_para_end_int:
         \__tag_check_para_end_show:nn{red}{} %debug: show para
         \tag_struct_end:
     }
  }
\ExplSyntaxOff

\begin{document}

% the last line before align must be completely full.
Cras nec ante. Pellentesque a nulla. Cum sociis natoque penatibus et
magnis dis parturient montes, nascetur ridiculus mus. Aliquam tincidunt urna.
Nulla ullamcorper vestibulum turpis. Pellentesque cursus luctus mauris. Pellentesque:
\begin{align}
\frac{d\Gamma}{dt} &= \frac{d}{dt} \int_{\mathcal{C}} \mathbf{u} \cdot d\mathbf{r}\\
				   &= \int_{\mathcal{C}} \frac{D\mathbf{u}}{Dt} \cdot d\mathbf{r} + \underbrace{\int_{\mathcal{C}} \mathbf{u}\cdot d\biggl( \frac{d\mathbf{r}}{dt}\biggr)}_{=\, 0} \\[-2pt]
                   &= \iint_{\mathcal{S}} \nabla \times \frac{D\mathbf{u}}{Dt}  \cdot d\mathbf{A}\\
                   &= \iint_{\mathcal{S}}  \nabla p \times \nabla \left( \frac{1}{\rho}\right) \cdot d\mathbf{A}
\end{align}

\end{document}

[FrankMittelbach]

Mathematical expressions shall be represented using either structure types defined in presentation MathML, as specified in ISO 32000-2:2020, 14.8.6.3, or as presentation MathML via the Associated Files mechanism specified in ISO 32000-2:2020, 14.13.6, or both.

To fulfil the requirement you need to provide a MathML-version of the equation that can then be included as associated file (the latex-lab-math documentation contains instructions for this). Without such a MathML you should not claim conformance with UA-2.

maybe that should be auto-detected and actually generate a warning at the end of the run?

[John02139]

Thanks, Ulrike. I should have set this a-4f, not ua-2, since I was switching between lualatex and pdftex.

The \unskip, I assume, needs to be added in latex-lab?

[FrankMittelbach]

The \unskip, I assume, needs to be added in latex-lab?

yes