LyX: labels with whitespaces [closed]

Question

I've noticed that LyX 2.4 does not like whitespaces inside the label field: it turns them into =000020 when converting into tex.

It's easy to reproduce. Insert a new label with a name A B and look at LaTeX Preview: \label{A=000020B}.

What are the actual, official, contemporary latex rules or problems regarding whitespaces inside \label and, if permitted, how to use them inside LyX?

Previously, Are LaTeX's label names case-sensitive? Can label names contain spaces? and What to consider when naming labels to prevent errors? suggested that whitespaces are allowed. I wonder then why LyX 2.4 is stricter.

Update. The accepted Answer has completely addressed the problem of the whitespaces in the latex label names, particularly when used by refstyle as it turns out, and how it's handled in the current and future versions of LyX. Therefore, I don't mind this Question to be "Closed" now. Thank you!

Answer 1

It turned out that LyX 2.4 escaped label names for compatibility with refstyle's formatted references:

\label{sec:A B}
 ...
\secref{A B} % can't find the label sec:AB -- refstyle has gobbled the whitespace!

1. LaTeX, refstyle restriction

I received an answer from the refstyle maintainer (Thank you, Daniel!) as follows (emphasis is mine):

"The main command in refstyle that cycles through a list of references (and a single reference) is:

\def\RS@ref#1[#2]#3{%
    \begingroup
        \RS@setkeys{RS@#1}{#2}%
        \@safe@activestrue%
        \edef\RS@tmpa{\zap@space#3 \@empty}%
        \@safe@activesfalse%
        \edef\RS@tmpa{\noexpand\RS@@ref{#1} \RS@tmpa,\relax\noexpand\@eolst}%
        \RS@tmpa%
    \endgroup}

It removes spaces and was intended for the following scenario, and that is how many people write a list of references with spaces in between

\secref(aaa, bbb, ccc) -> \ref{sec:aaa}, \ref{sec:bbb}, \ref{sec:ccc}

If the \zap@space part is removed then we have the wrong reference:

\secref(aaa, bbb, ccc) -> \ref{sec:aaa}, \ref{sec: bbb}, \ref{sec:
ccc}

The refstyle package cannot distinguish between a space in a list and a space in a reference. If I change that it will break a lot of old documents. The second point is that in standard latex, spaces in labels is a newish thing. It was not always there. Also note even if you put 10 spaces in a row in a label, latex only passes one through to the definition - see the .aux file. I think it is better to use an underscore _ or include your label in brackets {aaa}".

-- Danie Els

2. LyX, workaround

The extra brackets solution is committed into main by a LyX developer. Thank you, Jürgen!

\label{sec:A B}
 ...
\secref{A B} % can't find the label sec:AB -- refstyle has gobbled the whitespace!
 
\secref{{A B}} % works!

"Actually, considering all eventualities, this might be the best solution, as the problem only concerns refstyle's formatted ref commands. All other solutions that I could think of add unnecessary complication... Good, I committed to master". -- Jürgen