LaTeX: image using width set at 10% in nested lists or nested quoted paragraphs gets smaller and smaller

[jfbu]

Describe the bug

When using :width: 10% the effective dimension decreases in quoted paragraphes or list items. The result is counter-intuitive, because the text font size keep being the same only the effective text width diminishes. But surely 10% should refer either to page width or to text area width.

How to Reproduce

===================
 FOO documentation
===================


image in quoted paragraphs using width at 10%
=============================================

|sphinx|

 |sphinx|

  |sphinx|

   |sphinx|

    |sphinx|

     |sphinx|

      |sphinx|


image in nested lists using width at 10%
========================================

1. |sphinx|

   1. |sphinx|

      1. |sphinx|

         1. |sphinx|

            we stop here, else needed to use ``'maxlistdepth'`` of
            ``latex_elements`` to avoid LaTeX error about too many
            levels of nesting.

.. |sphinx| image:: img.png
            :width: 10%

Environment Information

Platform:              darwin;
Python version:        3.13.3 (v3.13.3:6280bb54784, Apr  8 2025, 10:47:54) [Clang 15.0.0 (clang-1500.3.9.4)])
Python implementation: CPython
Sphinx version:        8.3.0+/e1bd9cb38
Docutils version:      0.21.2
Jinja2 version:        3.1.6
Pygments version:      2.19.1

Sphinx extensions

Additional context

As per #13661, the cause is that Sphinx translates 10% into 0.100\linewidth.

[gmilde]

The specification is a bit vague:

Percentage values are relative to other values, depending on the context in which they occur.

The behaviour is currently the same in HTML and LaTeX: a width value of 10% sets the element width to 10% of the parent element.

While the current behaviour may appear odd in the specific examples above, it works fine in use cases that set the width of an image or table to 100%:

Percentage values in quotes and lists
=====================================

.. image:: img.png
   :width: 100%
   :height: 1em

In Docutils, 100% wide images in text body, quote, and list 
match the width of the respective text block. 
This means that their size depends on the context they appear in.
This behaviour is not universally expected:

   .. image:: img.png
      :width: 100%
      :height: 1em

   I do not think it make sense in LaTeX that image sizes would
   mysteriously shrink while text font size is not modified.
   The HTML/CSS paradigm should not be followed too closely.

Problems with using ``\textwidth`` instead of ``\linewidth``:

* An image in a quote, list, table or similar using 100% of
  the document-wide ``\textwidth`` dimension will overflow.
  
  .. image:: img.png
     :width: 100%
     :height: 1em

* Smaller ratios will work but deviate from the result in HTML.
  Behaviour differences between HTML and LaTeX violate the 
  “Law of Least Astonishment”: 
       
      .. image:: img.png
         :width: 100%
         :height: 1em
   
      In short, this law states that every construct in the system should
      behave exactly as its syntax suggests. Widely accepted conventions
      should be followed whenever possible, and exceptions to previously
      established rules of the language should be minimal.

[jfbu]

Thanks @gmilde for comment. I will probably not push to deviate from \linewidth and this may get closed without (effective) change. Leaving open in case further opinions are expressed. I will postpone the milestone of #13661. The complexities of tabulary make me suspect I can find other counter-intuitive results. Tabulary tries to decide on the fly what the suitable "width" of the cell is, and it is a bit obscure how in the #13661 example with only one cell the image width ends up at about 10pt, i.e. the actual cell width is set to be at about 100pt.