/usr/share/javascript/mathjax/jax/element/ is in libjs-mathjax 2.6.1-1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/javascript/mathjax/jax/element/mml/
/usr/share/javascript/mathjax/jax/element/mml/jax.js
/usr/share/javascript/mathjax/jax/element/mml/optable/
/usr/share/javascript/mathjax/jax/element/mml/optable/Arrows.js
/usr/share/javascript/mathjax/jax/element/mml/optable/BasicLatin.js
/usr/share/javascript/mathjax/jax/element/mml/optable/CombDiacritMarks.js
/usr/share/javascript/mathjax/jax/element/mml/optable/CombDiactForSymbols.js
/usr/share/javascript/mathjax/jax/element/mml/optable/Dingbats.js
/usr/share/javascript/mathjax/jax/element/mml/optable/GeneralPunctuation.js
/usr/share/javascript/mathjax/jax/element/mml/optable/GeometricShapes.js
/usr/share/javascript/mathjax/jax/element/mml/optable/GreekAndCoptic.js
/usr/share/javascript/mathjax/jax/element/mml/optable/Latin1Supplement.js
/usr/share/javascript/mathjax/jax/element/mml/optable/LetterlikeSymbols.js
/usr/share/javascript/mathjax/jax/element/mml/optable/MathOperators.js
/usr/share/javascript/mathjax/jax/element/mml/optable/MiscMathSymbolsA.js
/usr/share/javascript/mathjax/jax/element/mml/optable/MiscMathSymbolsB.js
/usr/share/javascript/mathjax/jax/element/mml/optable/MiscSymbolsAndArrows.js
/usr/share/javascript/mathjax/jax/element/mml/optable/MiscTechnical.js
/usr/share/javascript/mathjax/jax/element/mml/optable/SpacingModLetters.js
/usr/share/javascript/mathjax/jax/element/mml/optable/SuppMathOperators.js
/usr/share/javascript/mathjax/jax/element/mml/optable/SupplementalArrowsA.js
/usr/share/javascript/mathjax/jax/element/mml/optable/SupplementalArrowsB.js