docs: def content_val(self, ymldata=None, messages=None):
          """Validates the Telemetry Dictionary to ensure the contents for each of the fields
          meets specific criteria regarding the expected types, byte ranges, etc."""
  
          # Turn off the YAML Processor
          log.debug("BEGIN: Content-based validation of Telemetry dictionary")
          if ymldata is not None:
              tlmdict = ymldata
          else:
              tlmdict = tlm.TlmDict(self._ymlfile)
  
          try:
              # instantiate the document number. this will increment in order to
              # track the line numbers and section where validation fails
              docnum = 0
  
              # boolean to hold argument validity
              fldsvalid = True
  
              # list of rules to validate against
              rules = []
  
              ### set the packet rules
              #
              # set uniqueness rule for packet names
              rules.append(UniquenessRule('name', "Duplicate packet name: %s", messages))
  
              ###
              # Loop through the keys and check each PacketDefinition
              for key in tlmdict.keys():
                  pktdefn = tlmdict[key]
                  # check the telemetry packet rules
                  for rule in rules:
                      rule.check(pktdefn)
  
                  # list of field rules to validate against
                  fldrules = []
  
                  ### set rules for telemetry fields
                  #
                  # set uniqueness rule for field name
                  fldrules.append(UniquenessRule('name', "Duplicate field name: " + pktdefn.name + ".%s", messages))
  
                  # set type rule for field.type
                  fldrules.append(TypeRule('type', "Invalid field type for field: " + pktdefn.name + ".%s", messages))
  
                  # set field size rule for field.type.nbytes
                  fldrules.append(TypeSizeRule('nbytes', "Invalid field size for field: " + pktdefn.name + ".%s", messages))
  
                  # set field enumerations rule to check no enumerations contain un-quoted YAML special variables
                  fldrules.append(EnumRule('enum', "Invalid enum value for field: " + pktdefn.name + ".%s", messages))
                  #
                  ###
  
                  flddefns = pktdefn.fields
                  for fld in flddefns:
                      # check field rules
                      for rule in fldrules:
                          rule.check(fld)
  
                  # check if field rule failed, if so set the validity to False
                  if not all(r.valid is True for r in fldrules):
                      fldsvalid = False
  
              log.debug("END: Content-based validation complete for '%s'", self._ymlfile)
  
              # check validity of all packet rules and field validity
              return all(rule.valid is True for rule in rules) and fldsvalid
  
          except util.YAMLValidationError, e:
              # Display the error message
              if messages is not None:
                  if len(e.message) < 128:
                      msg = "Validation Failed for YAML file '" + self._ymlfile + "': '" + str(e.message) + "'"
                  else:
                      msg = "Validation Failed for YAML file '" + self._ymlfile + "'"
  
                  log.error(msg)
                  self.ehandler.process(self.ehandler.doclines, e, messages)
                  return False