multline env ignores \zlabel

[kia999]

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Brief outline of the bug

I noted that \zlabel introduced by zref package is ignored inside multline environment, it does not write \zref@newlabel to aux file. MWE is given below. I reported this 'feature' to zref repository but was answered that this is bug (or a feature) in amsmath.

Minimal example showing the bug

\documentclass[a4paper]{article}
\usepackage{amsmath}
\usepackage[user]{zref}

\begin{document}

\begin{equation}
\zlabel{eq:01}
E=mc^{2}
\end{equation}

\begin{multline}
\zlabel{eq:02}
W = \int \vec{\xi}\cdot \vec{F}(\vec{\xi}) ,d^{3}x
=
\
\iint \ldots
\end{multline}

First Eq.\zref{eq:01}, second Eq.\zref{eq:02}.
\end{document}

## Log file (required) and possibly PDF file  

!! Use drag-and-dro
[test-zref.log](https://github.com/latex3/latex2e/files/4179097/test-zref.log)
[test-zref.log](https://github.com/latex3/latex2e/files/4179101/test-zref.log)
[test-zref.pdf](https://github.com/latex3/latex2e/files/4179103/test-zref.pdf)


p  (remember: .log file is required) !!

[davidcarlisle]

For the record this is
ho-tex/zref#4

Note that as a core package amsmath can't really directly support a specific contributed package like zref (as would have been reported if the test file here had used the latexbug package as requested).

However it is (perhaps) possible that amsmath could make a hook available to make it easier for zref to detect when to write to the aux file. In the meantime a workaround as suggested by @u-fischer in the linked report is available.

[stale]

This issue has been automatically marked as stale because it has not had recent activity.

[FrankMittelbach]

to look again when there is a new hook management for LaTeX