Semantics of Content Elements

• Elements can use the definitonURL to override default semantics (eg, infix, postfix)
• Recommendation includes a formalism for defining semantics
• Other specifications through csymbol:

<!-- reference to OpenMath definition of Bessel function -->
<apply>
  <csymbol encoding="OpenMath" 
    definitionURL="http://www.openmath.org/cd/BesselFunctions.ocd">
    <msub><mi>J</mi><mn>0</mn></msub>
  </csymbol>
  <ci>y</ci>
</apply>