"An mpadded element renders the same as its child content, but with the size of the child's bounding box and the relative positioning point of its content modified according to mpadded's attributes."
MathJax uses mpadded to implement many LaTeX commands.
Created attachment 273971 [details]
A first patch without the expectations.
Comment on attachment 273971 [details]
This patch was intended for bug 155435.
Basic support was added in bug 155792. Currently, we do not implement:
- pseudo-unit such as width="3width"
- negative lspace like lspace="-4px"