code: public boolean isLinkField(String fieldName) {
          FieldDefinition fieldDef = m_fieldDefMap.get(fieldName);
          return fieldDef != null && fieldDef.isLinkField();
      }
docs: Return true if this table definition possesses a FieldDefinition with the given name
  that defines a Link field.
  
  @param   fieldName   Candidate field name.
  @return              True if the name is a known Link field, otherwise false.