Steps to replicate the issue (include links if applicable):

• Set user preference to "Client side MathJax rendering (for browsers with limited MathML support)"
• View the page https://en.wikipedia.org/wiki/Help:Displaying_a_formula

What happens?:

The following latex expressions fail.

• <math>\tilde{a}</math> gives "mover" red writing on yellow background
• <math>^\wedge</math> gives " msup" red writing on yellow background
• <math>f(n) =\begin{cases} n/2, & \text{if }n\text{ is even} \\3n+1, & \text{if }n\text{ is odd}\end{cases}</math> "math input error"

• <math>\boldsymbol{\alpha \beta \gamma \delta \epsilon \zeta \eta \theta}</math> "math output error"

• <math> \boldsymbol{\iota \kappa \lambda \mu \nu \xi \omicron \pi}</math> "math output error"

• <math> \boldsymbol{\rho \sigma \tau \upsilon \phi \chi \psi \omega}</math> "math output error"

• <math> \boldsymbol{\varepsilon\digamma\varkappa\varpi}</math> "math output error"

• <math> \boldsymbol{\varrho\varsigma\vartheta\varphi}</math> "math output error"

• <math> \text{if }n\text{ is even}</math> "Math input error"

• <math> a \text{ } b</math> "Math input error"
• <math>( \nabla \times \mathbf{F} ) \cdot {\mathrm d}\mathbf{S} = \oint_{\partial S} \mathbf{F} \cdot {\mathrm d}\boldsymbol{\ell}</math> "math output error"
• <math>\oint_C \mathbf{B} \cdot {\mathrm d} \boldsymbol{\ell} = \mu_0 </math> "math output error"
• <chem>\mu-Cl</chem> "Math output error"
• <chem>[Fe(\eta^5-C5H5)2]</chem> "Math output error"
• <math chem>\begin{align}\overbrace{\ce{2Fe3O4}}^{\text{magnetite}} + \ce{1/2 O2 ->}\ &{\color{Brown}\overbrace{\ce{3(\lambda{-}Fe2O3)}}^{\text{maghemite}}}\\ \underbrace{\ce{2Fe3O4}}_{\text{magnetite}} + \ce{1/2 O2 ->}\ {\color{Red}\underbrace{\ce{3(\alpha{-}Fe2O3)}}_{\text{hematite}}} \end{align}</math> Math output error

problems with old mhchem syntax (ignored)

• <chem>{C_\mathit{x}H_\mathit{y}} + \mathit{z}O2 -> {\mathit{x}CO2} + \frac{\mathit{y}}{2}H2O</chem> Failed to parse (syntax error): {\displaystyle \ce{{C_\mathit{x}H_\mathit{y}} + \mathit{z}O2 -> {\mathit{x}CO2} + \frac{\mathit{y}}{2}H2O}}
• <chem>A ->[{}\atop x] B</chem> Failed to parse (syntax error): {\displaystyle \ce{A ->[{}\atop x] B}}
• <chem>A ->[{}\atop\ce{+H2O}] B</chem> Failed to parse (syntax error): {\displaystyle \ce{A ->[{}\atop\ce{+H2O}] B}}

Open sub-tasks

• T390260 @JeanCASPAR (critical)
• T405439
• T401718

• Review the entire page again
• \grave{a} too big T409110
• \hat and \widehat look the same
• \vec is too large
• \P is messed up
• \sqrt[3]{x} 3 is too small
• c in large dfrac example is wrong
• \smallmatrix is wrong

What should have happened instead?:

All equations rendered correctly

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):

Google Chrome 128.0.6613.138 (Official Build) (64-bit) (cohort: Stable)