centerbaseline=false
mml=<math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mfenced><mrow><msub><mi mathvariant="normal">x</mi><mn>1</mn></msub><mo>+</mo><msub><mi mathvariant="normal">x</mi><mn>2</mn></msub><mo>+</mo><msub><mi mathvariant="normal">x</mi><mn>3</mn></msub><mo>+</mo><msub><mi mathvariant="normal">x</mi><mn>4</mn></msub></mrow></mfenced><mn>4</mn></mfrac><mo>=</mo><mn>15</mn></math>