Enable "MathML (experimental; no images)" in Special:Preferences → Apperance → Math. Then preview a page with the contents <math>K = \operatorname{ker}(A)</math>.
This renders with too much space before and after "ker" in Firefox and Chrome:
Server-side SVG and client-side MathJax look good:
Here's a real-world example, where the spacing is particularly bad:
To fix this, I suggest using an <mi> element for \operatorname{ker} instead of <mo> since we already use <mi> for special functions like \sin. Temml.org also uses <mi> for \operatorname{ker}.
