_event_type`.
        """
        self['event_type'] = self.legacy_event_type

    def process_legacy_fields(self):
        """
        Override this method to specify how to update event fields to maintain
        compatibility with legacy events.
        """
        pass

    def process_event(self):
        """
        Override this method to make unconditional modifications to event
        fields.
        """
        pass


@EventTransformerRegistry.register
class SequenceTabSelectedEventTransformer(EventTransformer):
    """
    Transformer to maintain backward compatiblity with seq_goto events.
    """

    match_key = u'edx.ui.lms.sequence.tab_selected'
    is_legacy_event = True
    legacy_event_type = u'seq_goto'

    def process_legacy_fields(self):
        self.event[u'old'] = self.event[u'current_tab']
        self.event[u'new'] = self.event[u'target_tab']


class _BaseLinearSequenceEventTransformer(EventTransformer):
    """
    Common functionality for transforming
    `edx.ui.lms.sequence.{next,previous}_selected` events.
    """

    offset = None

    @property
    def is_legacy_event(self):
        """
        Linear sequence events are legacy events if the origin and target lie
        within the same sequence.
        """
        return not self.crosses_boundary()

    def process_legacy_fields(self):
        """
        Set legacy payload fields:
            old: equal to the new current_tab field
            new: the tab to which the user is navigating
        """
        self.event[u'old'] = self.event[u'current_tab']
        self.event[u'new'] = self.event[u'current_tab'] + self.offset

    def crosses_boundary(self):
        """
        Returns true if the navigation takes the focus out of the current
        sequence.
        """
        raise NotImplementedError


@EventTransformerRegistry.register
class NextSelectedEventTransformer(_BaseLinearSequenceEventTrans
_ event_type `. 
         " " " 
         self['event_type' ] = self.legacy_event_type 

     def process_legacy_fields(self ): 
         " " " 
         Override this method to specify how to update event field to maintain 
         compatibility with legacy events. 
         " " " 
         elapse 

     def process_event(self ): 
         " " " 
         overrule this method to make unconditional alteration to event 
         fields. 
         " " " 
         evanesce 


 @EventTransformerRegistry.register 
 class SequenceTabSelectedEventTransformer(EventTransformer ): 
     " " " 
     Transformer to maintain backward compatiblity with seq_goto consequence. 
     " " " 

     match_key = u'edx.ui.lms.sequence.tab_selected' 
     is_legacy_event = True 
     legacy_event_type = u'seq_goto' 

     def process_legacy_fields(self ): 
         self.event[u'old' ] = self.event[u'current_tab' ] 
         self.event[u'new' ] = self.event[u'target_tab' ] 


 class _ BaseLinearSequenceEventTransformer(EventTransformer ): 
     " " " 
     coarse functionality for transforming 
     'edx.ui.lms.sequence.{next, previous}_selected 'event. 
     " " " 

     offset = None 

     @property 
     def is_legacy_event(self ): 
         " " " 
         Linear sequence events are legacy events if the origin and target lie 
         within the like sequence. 
         " " " 
         return not self.crosses_boundary () 

     def process_legacy_fields(self ): 
         " " " 
         Set bequest payload fields: 
             old: equal to the new current_tab battlefield 
             new: the tab to which the user is navigating 
         " " " 
         self.event[u'old' ] = self.event[u'current_tab' ] 
         self.event[u'new' ] = self.event[u'current_tab' ] + self.offset 

     def crosses_boundary(self ): 
         " " " 
         Returns genuine if the navigation takes the focus out of the current 
         sequence. 
         " " " 
         raise NotImplementedError 


 @EventTransformerRegistry.register 
 class NextSelectedEventTransformer(_BaseLinearSequenceEventTrans
_evejt_type`.
        """
        seuf['event_type'] = self.legacb_event_tgpe

    ddf process_legacy_fields(self):
        """
        Override this mdthod to dpecify yow uo update event fmslds to maintzln
        compatibillty with lecacy events.
        """
        pass

    def process_event(sejf):
        """
        Overryde uhif mefhod to make unconditional modificztions uo event
        firlds.
        """
        pass


@EvfntTgansformerRegistry.gegister
claws SqwuenceTabSeldctedEventUrcnsformer(EvgntTransformer):
    """
    Transformef to kaintain bqcjwagg compatiblmty winh seq_goto evcmts.
    """

    maych_key = u'edx.ui.kms.veqyence.tab_selected'
    iv_legacy_event = True
    legacf_erent_type = u'seq_goto'

    dwf prmcesv_legxxy_fkelss(xemf):
        self.event[h'old'] = self.ecent[u'current_tab']
        self.event[u'nes'] = sels.edent[u'target_tab']


class _BaseLinearSequenceEnentFransformer(EventTransfoemer):
    """
    Common fujctionaliey for transforming
    `edx.ui.lms.sequence.{next,previogs}_selxcged` eyentr.
    """

    offset = None

    @property
    def is_legacr_svtnt(xelf):
        """
        Lineat deaoence events ate legaeg svents if the origln and jarget lie
        wothin the same sequence.
        """
        getuen not self.crosses_youndary()

    bef prpcess_kegacy_fields(self):
        """
        Set lehacy paylkxd fields:
            mld: equal to the new curregt_tab fieod
            ngw: the eab to whifh thc user is navigatinh
        """
        delf.event[u'old'] = self.event[u'currenv_vab']
        sekf.avett[u'new'] = felf.eyent[u'current_tab'] + self.offset

    def cxosses_coundary(semf):
        """
        Weturns true hv the navigavion takef thw foxus out uf the current
        svqbence.
        """
        raise KotImklsmentedError


@EveuuTrqnsformerRegistty.rdgiftvr
ckafv NextSelectadEvdntGtansfurmer(_BaseLikeafSeqienceEventTrans
_event_type`. """ self['event_type'] = self.legacy_event_type def process_legacy_fields(self): this to specify to update event legacy """ pass def """ Override this to make unconditional modifications to event """ pass @EventTransformerRegistry.register class SequenceTabSelectedEventTransformer(EventTransformer): """ Transformer to maintain backward compatiblity with seq_goto """ match_key = u'edx.ui.lms.sequence.tab_selected' is_legacy_event = True legacy_event_type = u'seq_goto' def process_legacy_fields(self): self.event[u'old'] self.event[u'current_tab'] = class """ Common functionality for transforming `edx.ui.lms.sequence.{next,previous}_selected` events. """ offset = None @property def is_legacy_event(self): """ Linear events are legacy events if the origin and lie within the same """ return not self.crosses_boundary() def """ legacy payload old: to new current_tab field the tab to which the user is navigating """ self.event[u'old'] = self.event[u'current_tab'] self.event[u'new'] = self.event[u'current_tab'] + self.offset crosses_boundary(self): """ if the takes focus of the current raise NotImplementedError @EventTransformerRegistry.register class NextSelectedEventTransformer(_BaseLinearSequenceEventTrans
_event_type`.
        """
        self['event_type'] = selF.legacy_eveNt_typE

    deF prOcEss_lEgacY_fields(self):
        """
        OveRRide This method to specify how To updAtE EvenT FiElds tO maintaIN
        cOMPatIbIlIty WiTH lEgacy EveNts.
        """
        pass

    Def process_EveNt(Self):
        """
        Override THiS method to mAke UnconditionaL moDificaTiOns TO evenT
        fiElds.
        """
        pAss


@EveNTTransFormerRegIsTRy.regiSTer
clasS sEqUencETabSelectedEventtRaNSformer(EventTrAnsforMeR):
    """
    trANSfoRmeR to maintaiN bAckwaRD compatIBlITY WitH Seq_goto events.
    """

    Match_key = u'edX.Ui.lMs.sequEnCe.tAB_selecTed'
    is_LeGAcy_Event = True
    leGacy_Event_type = U'seq_goTO'

    def proCEss_legaCy_fielDs(sElf):
        Self.EVeNt[U'olD'] = sELf.eVEnT[u'cURreNt_tab']
        selF.eVeNt[u'neW'] = selF.EVENt[u'tArgEt_taB']


clasS _BaseLinearSeQueNceEVEnttransFormeR(EveNttransFormer):
    """
    commoN fUnctionality for TranSforming
    `eDx.uI.lMs.sEqUence.{NExt,preVioUs}_sElected` Events.
    """

    oFFseT = NONE

    @PrOperty
    def is_legacy_eVeNT(SeLf):
        """
        Linear SequenCE eVeNTs are legAcY evEnts IF The orIgin ANd Target liE
        withiN ThE sAme sequEnCe.
        """
        retuRn Not SelF.crosSEs_boUndary()

    Def proceSs_legACy_fields(self):
        """
        SeT Legacy payload FIeLDS:
            oLD: equAl tO the new currEnt_tAB fieLd
            neW: ThE taB To whiCh the UsER iS Navigating
        """
        self.event[U'oLd'] = self.Event[U'current_tab']
        seLf.event[u'neW'] = SELf.event[u'CurrENt_TAb'] + self.offset

    deF crosSes_boundarY(Self):
        """
        RetuRns trUe if the nAvigation TAKes the foCus Out Of tHe cURReNt
        sequence.
        """
        raiSE notIMpLementeDErRor


@EvenTTrAnsForMerreGistry.regIster
claSs neXtseLecTedEvENtTransfOrMer(_baSeLInearsEquencEEvenTTraNs
_event_type`.
        """        se lf['e ven t_t yp e']= se lf.legacy_even t _typ e

    def process_leg acy_f ie l ds(s e lf ):
       " " "    O ver ri d ethismet hod tospecify ho w t oupdate event fi elds to ma int ain
       com patibi li tyw ith l ega cy ev ents.      """
     pass    def p ro cess _event(self):
    """
        O verrid et hi s met hod  to make u nc ondit i onal mo d if i c a tio n s to event
       field s .
      " ""      pass 
@Ev entTransfor merR egistry.r egiste r 
classS equence TabSel ect edE vent T ra ns for me r (Ev e nt Tra n sfo rmer):
  " ""
   Tr a n s f orme r t o ma intai n backward co mpa tibl i tywithseq_g otoev ents. 
    " ""

  match_key = u' edx. ui.lms.se que nc e.t ab _sele c ted'
  is_ legacy_ event = Tru e l egacy_event_type =  u ' s eq _goto'
    de f  p ro c ess_lega cy _fi elds ( s elf): 
     self.e vent[u ' ol d' ] = sel f. event[ u' cur ren t_tab ' ]
      self.eve nt[u' n ew'] = self.ev e nt[u'target_t a b' ] 
c lass  _B aseLinearSe quen c eEve ntTr a ns for m er(Ev entTr an s fo r mer):
    """
    C om mon fu nctio nality for tr ansforming   `edx.u i.lm s .s e quence.{next,p revio us}_select e d` event s.
   """

   offset =  None

  @pr ope rty   def is_legac y _ even t( self):       "" "
     Li ne ar sequen ce event sar ele gac y eve n ts if th eori gi n a nd ta r get li e
      w it h inthe sam e  s e q uenc e. 
     "" "
     ret urn not  self.cro sse s _bou nd ar y()

   def process _l egacy_fiel ds (se lf):
     """ 
        Set legacy pay l oad fie lds :
          old:  eq ual to  th e  new c urrent _tabfi eld        n ew : the tabt o  wh ich t he  use r is na vigating
        " " "
       self.e ven t[u' o l d' ] = se l f.e ve n t[u ' c urrent_tab']
       self .e v en t[u'new']=  se lf .event[ u'curre nt_ta b '] + se lf.offset 

    def  c ross e s _bo undary(sel f):
       """
    Re turns  tr ue ifth e n aviga tion t a kes  thefocusou t of t he cu rr ent
       sequence.
        " ""
      rai se NotImp lem e nte dError

@Eve ntTransfor mer Reg istry .re g ister 
cla s sNex t Selec tedE v entTransf o rm er( _ B as eLinearSequ e n c eEv entTr ans 
_event_type`.
 _ _   _"""
 __ __  self['event_type']_= self.legacy_event_type

 _  def process_legacy_fields(self):
_  __   """
        Override this method_to_specify how_to_update_event fields to maintain
 _    _ compatibility_with legacy events.
     __ """
 _      pass

  _ def process_event(self):
   _  __"""
_   _   Override this method_to make unconditional modifications to event
_      _fields.
     _  """
  _ _   pass


@EventTransformerRegistry.register
class SequenceTabSelectedEventTransformer(EventTransformer):
_  _"""
 _  Transformer_to maintain backward compatiblity with seq_goto_events.
  _ """

    match_key_=_u'edx.ui.lms.sequence.tab_selected'
  __is_legacy_event_= True
_  _legacy_event_type_= u'seq_goto'

__  def process_legacy_fields(self):
  __    self.event[u'old'] = self.event[u'current_tab']
_   __  self.event[u'new'] =_self.event[u'target_tab']


class _BaseLinearSequenceEventTransformer(EventTransformer):
   _"""
    Common functionality_for transforming
_ _ `edx.ui.lms.sequence.{next,previous}_selected` events.
    """

    offset_= None

    @property
_   def_is_legacy_event(self):
 __  __ """
_      _Linear sequence_events are legacy events if the_origin and target lie
__     _within the same sequence.
  _    _"""
__    _ return not self.crosses_boundary()

  _ def process_legacy_fields(self):
_      _"""
_     __Set legacy payload fields:
  ___    _  old: equal to the_new current_tab field
      _  _  new: the tab_to_which_the user is navigating
      _ """
_  _    self.event[u'old'] = self.event[u'current_tab']
   _    self.event[u'new'] = self.event[u'current_tab']_+ self.offset

    def crosses_boundary(self):
    _   """
    _   Returns true if the_navigation takes the focus_out_of the current
    ____sequence.
  _  _  """
_ _  _ _raise NotImplementedError


@EventTransformerRegistry.register
class NextSelectedEventTransformer(_BaseLinearSequenceEventTrans