<mfrac>

The MathML <mfrac> element is used to display fractions.

<mfrac>numerator denominator</mfrac>

bevelled

Specifies the way the fraction is displayed. If true, the fraction line is bevelled, which means that numerator and denominator are displayed side by side and separated by a slash (/). Otherwise, if set to false (which is the default value), numerator and denominator are on top of each other.
This attribute is deprecated and will be removed in the future. Use U+2044 (fraction slash) instead.

class, id, style

Provided for use with stylesheets.

denomalign

The alignment of the denominator under the fraction. Possible values are: left, center (default), and right.
This attribute is deprecated and will be removed in the future. Use CSS text-align instead.

displaystyle

A Boolean value specifying whether more vertical space is used for displayed equations or, if set to false, a more compact layout is used to display formulas. The main effect is that larger versions of operators are displayed, when displaystyle is set to true. See also movablelimits on <mo>.

href

Used to set a hyperlink to a specified URI.

linethickness

The thickness of the horizontal fraction line. This attributes accepts any length values.
The values medium, thin, and thick are deprecated and will be removed in the future.

mathbackground

The background color. You can use #rgb, #rrggbb and HTML color names.

mathcolor

The text color and also the fraction line color. You can use #rgb, #rrggbb and HTML color names.

numalign

The alignment of the numerator over the fraction. Possible values are: left, center (default), and right.
This attribute is deprecated and will be removed in the future. Use CSS text-align instead.

Sample rendering:

Your browser rendering: $\raisebox{1ex}{$\frac{a}{b}$}\!\left/ \!\raisebox{-1ex}{$\frac{c}{d}$}\right.$

<math>
  <mfrac bevelled="true">
     <mfrac>
        <mi> a </mi>
        <mi> b </mi>
     </mfrac>
     <mfrac>
        <mi> c </mi>
        <mi> d </mi>
     </mfrac>
  </mfrac>
</math>