▁which ▁may ▁be ▁represented ▁by ▁icons ▁alone ▁( in ▁which ▁case ▁the ▁icons ▁are ▁col oured ▁as ▁the ▁frame ▁would ▁be ). ▁ ▁The ▁fill ▁is ▁the ▁area ▁within ▁a ▁symbol . ▁If ▁the ▁fill ▁is ▁assigned ▁a ▁colour , ▁it ▁provides ▁an ▁en hanced ▁( redu nd ant ) ▁presentation ▁of ▁information ▁about ▁the ▁affili ation ▁of ▁the ▁object . ▁If ▁colour ▁is ▁not ▁used , ▁the ▁fill ▁is ▁transparent . ▁A ▁very ▁few ▁icons ▁have ▁fills ▁of ▁their ▁own , ▁which ▁are ▁not ▁affected ▁by ▁affili ation . ▁ ▁The ▁icons ▁themselves , ▁finally , ▁can ▁be ▁understood ▁as ▁combinations ▁of ▁elementary ▁g lyph s ▁that ▁use ▁simple ▁composition ▁rules , ▁in ▁a ▁manner ▁rem in is cent ▁of ▁some ▁ide ographic ▁writing ▁systems ▁such ▁as ▁Chinese . ▁The ▁standard , ▁however , ▁still ▁attempts ▁to ▁provide ▁an ▁" ex ha ust ive " ▁listing ▁of ▁possible ▁icons ▁instead ▁of ▁lay ing ▁out ▁a ▁dictionary ▁of ▁component ▁g lyph s . ▁This ▁causes ▁oper ational ▁problems ▁when ▁the ▁need ▁for ▁an ▁un for ese en ▁symbol ▁ar ises ▁( part icular ly ▁in ▁MO OT W ), ▁a ▁problem ▁ex ac erb ated ▁by ▁the ▁administr atively ▁central ised ▁maintenance ▁of ▁the ▁sym b ology ▁sets . ▁ ▁When ▁rendering ▁symbols ▁with ▁the ▁fill ▁on , ▁AP P - 6 A ▁calls ▁for ▁the ▁frame ▁and ▁icon ▁to ▁be ▁black ▁or ▁white ▁( as ▁appropriate ▁for ▁the ▁display ). ▁When ▁rendering ▁symbols ▁with ▁the ▁fill ▁off , ▁AP P - 6