Change #1277186 had a related patch set uploaded (by C. Scott Ananian; author: C. Scott Ananian):

[mediawiki/core@master] ParsoidLanguageConverter: fix behavior of nested -{R|...}- rules

https://gerrit.wikimedia.org/r/1277186

I still wonder what is the intended behaviour for nested LC markup. It appears undocumented.

The current behavior (as far as I know) is:

-{[http://... -{paris.fr}-]}-

-{                   // Prevent any "display text" being converted
    [                // External link syntax
        http://...   // The link itself never being converted, even as the link display text
                     // The whitespace separator between the link target and the link display text
        -{           // Prevent the link display text being converted
            paris.fr // The original link display text
        }-
    ]
}-

The current behavior should be some kind of "unwrapping", so the "outer" unwrapping comes first, then the "inner".

In a nutshell: Just like the inline CSS styles.

-{                                 [        https://...  -{                                 Text     }-   ]     }-
<span style="background: #6a60b0;"><a href="https://,,,"><span style="background: #177860;">Text</span></a></span>

Change #1277186 merged by jenkins-bot:

[mediawiki/core@master] ParsoidLanguageConverter: fix behavior of nested -{R|...}- rules

https://gerrit.wikimedia.org/r/1277186

As described in the commit message:

Previously we were skipping the contents of "raw" rules entirely, but
we are expected to convert rules inside them, just not convert text.

Tests added to demonstrate this behavior.