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nLab > nLab Technical Matters: slash command, used e. g. for Feynman slash notation, silently fails to render

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    • CommentRowNumber1.
    • CommentAuthorjesuslop
    • CommentTimeJul 5th 2025

    One can see in the page Feynman slash notation that the LaTeX command \slash{...} is used but it fails to render anything, it just fails silently, as if it were a redefinition of \nop{...}. This can be not just a problem of that page if usage spills to more places. Stripping slashing generates formulas that are wrong but maybe not obviously so, leading to a potentially insidious problem.

    • CommentRowNumber2.
    • CommentAuthorUrs
    • CommentTimeJul 5th 2025
    • (edited Jul 5th 2025)

    When I first read your message, also for me the slash wasn’t showing. But now, a minute later, it is.

    Therefore I suspect that this is not an issue specific to \slash but rather an instance of the known bug which has been with us for some time now:

    It frequently happens upon loading of a page that parenthesis in formulas and math operators are not being rendered: One sees the mathematical variables, but not the rest of the formulas that they are part of.

    In such a situation, any step that forces the page to re-render makes the missing symbols appear (such as reloading the page or scrolling down a full screen height and back up again).

    This is indeed annoying, yes, to say the least.

    We have discussed the issue before somewhere on the nForum: here, though without coming to a conclusion.

    I could try to contact the technical team again to see if they have any idea.

    • CommentRowNumber3.
    • CommentAuthorUrs
    • CommentTimeJul 5th 2025

    Sorry, I take that back. It’s a different issue now:

    Further testing shows that I consistently see the slash on the nLab pages when using Firefox (on Windows, in my case) but not when using Chrome (either on Windows or on Android).

    • CommentRowNumber4.
    • CommentAuthorUrs
    • CommentTimeJul 5th 2025

    Further experimenting in the Sandbox:

    Tried what happened when we hack the effect by typing “$D\!\!\!\!\!/$”.

    Again, this comes out fine with Firefox, but not with Chrome: the latter ignores the negative whitespace “\!”.

    So it seems clear that it is a rendering issue with Chrome (Blink). Maybe somebody wants to file a bug report to them.

    • CommentRowNumber5.
    • CommentAuthorDmitri Pavlov
    • CommentTimeJul 5th 2025
    • (edited Jul 5th 2025)
    Re #4: The MathML code uses

    <menclose notation="updiagonalstrike">

    which is not implemented in Chromium, by choice.

    This is a controversial MathML element, as far as I can see, there are discussions to possibly remove it from MathML or at least redesign it:

    https://github.com/w3c/mathml-core/issues/274
    https://github.com/w3c/mathml/issues/105
    https://github.com/mdn/browser-compat-data/pull/23588

    More specifically, menclose is not in MathML Core: https://w3c.github.io/mathml/#presm_menclose

    As far as I understand, Chromium intends to support MathML Core, but not the entire MathML.

    What works correctly in both Firefox and Chromium is combining Unicode characters: D̸ and d̸ (see Sandbox)
    • CommentRowNumber6.
    • CommentAuthorUrs
    • CommentTimeJul 5th 2025
    • (edited Jul 5th 2025)

    Thanks, that’s useful.

    Your unicode encoding works for me with Chrome on Win!

    But it still does not work:

    (1.) with Chrome on Android,

    (2.) generally, with any browser (a.) here on the nForum and (b.) in math mode.

    (In the latter cases the negative whitespace is insufficient: the slash hardly touches the preceding letter.)

    Here is a table with some variants. Now that I test-view this on the nForum, I see that here on the nForum \slash is invisible even with Firefox.

    code rendering
    $\slash{D}$
    $D\!\!\!\!\!/$ D/
    $&#119863;&#824;$ 𝐷̸
    $\text{&#119863;&#824;}$ 𝐷̸
    $\text{&#8706;&#824;}$ ∂̸

    So we don’t seem to have any satisfactory solution so far.

    • CommentRowNumber7.
    • CommentAuthorDmitri Pavlov
    • CommentTimeJul 6th 2025
    • (edited Jul 6th 2025)
    These appear to work in both Firefox and Chrome:

    <div style='position: absolute; z-index:100;'>&thinsp;&thinsp;/</div>$D$

    <div style='position: absolute; z-index:100;'>&thinsp;/</div>$\partial$
    • CommentRowNumber8.
    • CommentAuthorUrs
    • CommentTimeJul 6th 2025

    Thanks. I guess this still doesn’t work inside a math environent, though.

    We’d need some replacement for the \slash appearing in a display context like $$ \slash{D} = \gamma^\my \partial_\mu $$.

    But maybe the issue is not worth the effort. I don’t think that the slash notation is used much at all on nLab pages, besides the page dedicated to it.

    I’ll just add a warning there now and then maybe we can safely leave it at that.

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