class_docstr: A class for representing multivariate rational function fields. 
docstr: Returns denominator of ``a``. 
code: def denom(self, a):
      """Returns denominator of ``a``."""
      return a.denom
  
imports: from sympy.polys.domains.compositedomain import CompositeDomain
  from sympy.polys.domains.field import Field
  from sympy.polys.polyerrors import CoercionFailed, GeneratorsError
  from sympy.utilities import public
label_desc: Use image node_id 30 for calling the FractionField obj's underlying member method code with example usage: obj.denom(a) and returns: a