MathJax Not Rendering Inside <details> Without Newline After <summary>

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The discussion addresses an issue where MathJax expressions inside <details> HTML tags fail to render unless a newline is placed immediately after the <summary> tag. Ethsim2 reports this behavior, noting it affects both inline and block math and is undocumented. j.jaffeux suggests using the [details] bbcode instead, which avoids the issue. sam clarifies that this is not a bug but a limitation of CommonMark’s handling of mixed HTML and Markdown, making the behavior expected rather than erroneous.

1

Hi — this is a follow-up to my earlier post:

I’ve identified that MathJax expressions inside <details> blocks do not render unless a newline is inserted immediately after the <summary> tag.

Minimal reproduction:

This does not render:

<details><summary>Example</summary>
$$
x^2 + y^2 = z^2
$$
</details>

This does render:

<details><summary>Example</summary>

$$
x^2 + y^2 = z^2
$$
</details>

Notes:

  • This behavior is unintuitive and undocumented.
  • It affects both inline and block MathJax.
  • ChatGPT tells me it “Tested on Discourse 3.2.0beta3 with default settings”.

Could this be made more robust or documented somewhere for users relying on math formatting?

2

You wouldn’t have this problem if you were using details block which is the recommended way:

[details="Example"]
$$
x^2 + y^2 = z^2
$$
[/details]
3

ah, it’s probably best to not fix this topic then

it’s ChatGPT that needed fixing :rofl:

4

Yeah this is not a bug, its a limitation/design of CommonMark

Mixing HTML and Markdown has some very specific and somewhat surprising rules.