In general one can use the command texdoc <package-name> on the command line to get documentation about a specific package. Instead of using texdoc on your machine you can also use the online version at https://texdoc.org.
The following list gives an overview about different packages related to tagging and some details on the contents of each:
ltnews.pdf (or ltnews<number>.pdf)
LaTeX news (one for each LaTeX release) discusses relevant changes and enhancements in LaTeX in particular also updates and improvements for tagging of documents
documentmetadata-support-code.pdf
Contain details about \DocumentMetadata and the various supported settings, e.g. pdfstandard, lang, pdfversion
latex-lab-graphic.pdf
Details on graphics tagging - including description for artifact, alt, actualtext, samples for tikz
latex-lab-math.pdf
Details on math tagging and special treatment capturing math contents
latex-lab-table.pdf
Details on table tagging - which table types are supported, which not; headers and rows, columns, etc.
blocks-doc.pdf (or blocks-code.pdf)
How to declare and customize block-level environments, such as center or lists, etc.
l3pdfmeta.pdf
Details on PDF-standards (from the perspective of LaTeX implementation)
tagpdf.pdf
Documentation of low-level tagging commands and methods; description of \tagpdfsetup and the key/values it supports
For example, texdoc ltnews41 opens the LaTeX news for release 2025-06-01. Without the number, a document with the release notes from all releases since 1994 is opened. Similarly, texdoc blocks-doc will open the documentation on tagging of block-level environments for you.
To find a complete list of the currently available documents from the latex-lab please look at: https://ctan.org/tex-archive/macros/latex-dev/required/latex-lab.
Please also note that most of the documentation (as well as this page) is “work in progress”. Therefore, the list above might not completely reflect the current status of implementation.
If you have a tagged PDF document and want to check the of the tagging you can try