Add comment about extensions to validator-main.protoascii.
Add comment about extensions to validator-main.protoascii.

yandex-pcode/amphtml,danielrozenberg/amphtml,taboola/amphtml,comScore/amphtml,lzanol/amphtml,spotxchange/amphtml,DAC-f1h-dev/amphtml,lzanol/amphtml,Mobusi-ads/amphtml,erwinmombay/amphtml,techhtml/amphtml,sortable/amphtml,zhucl/amphtml,rajkumarsrk/amphtml,devjsun/amphtml,arealit/amphtml,burtcorp/amphtml,Gregable/amphtml,Lith/amphtml,rsimha-amp/amphtml,rsimha-amp/amphtml,adiant/amphtml,Mixpo/amphtml,luciancrasovan/amphtml,laterpay/amphtml,shawnbuso/amphtml,zhangsu/amphtml,zhouyx/amphtml,keithwrightbos/amphtml,AaronCritchley/amphtml,comScore/amphtml,src-code/amphtml,tdrl/amphtml,jpettitt/amphtml,BenDz/amphtml,clawr/amphtml,erwinmombay/amphtml,criteo-forks/amphtml,cvializ/amphtml,aghassemi/amphtml,triplelift/amphtml,spotxchange/amphtml,JuliusThms/amphtml,dvoytenko/amphtml,alanorozco/amphtml,rsimha-amp/amphtml,nekodo/amphtml,lzanol/amphtml,media-net/amphtml,kixer-com/amphtml,pedjoni8/amphtml,powdercloud/amphtml,wjfang/amphtml,nexxtv/amphtml,alanorozco/amphtml,BrightcoveOS/amphtml,ampproject/amphtml,ADITION/amphtml,dotandads/amphtml,mkhatib/amphtml,koshka/amphtml,ColombiaAnalytics/amphtml,nexxtv/amphtml,fullspeed-sp/amphtml,gumgum/amphtml,cory-work/amphtml,powdercloud/amphtml,zhucl/amphtml,powdercloud/amphtml,ampproject/amphtml,jridgewell/amphtml,engtat/amphtml,sklobovskaya/amphtml,kamtschatka/amphtml,ecoron/amphtml,yandex-pcode/amphtml,dvoytenko/amphtml,arealit/amphtml,rifler/amphtml,mhc-gh/amphtml,voyagegroup/amphtml,camelburrito/amphtml,comScore/amphtml,sklobovskaya/amphtml,DarXector/amphtml,dotandads/amphtml,comScore/amphtml,sortable/amphtml,DistroScale/amphtml,interspacejp/amphtml,donttrustthisbot/amphtml,yandex-pcode/amphtml,Lith/amphtml,ecoron/amphtml,zhucl/amphtml,luciancrasovan/amphtml,triplelift/amphtml,jlucero-contentad/amphtml,jpettitt/amphtml,honeybadgerdontcare/amphtml,erwinmombay/amphtml,adiant/amphtml,jpettitt/amphtml,sklobovskaya/amphtml,jpettitt/amphtml,jdelhommeau/amphtml,galeksic/amphtml,chaveznvg/amphtml,zhangsu/amphtml,src-code/amphtml,jasti/amphtml,DAC-f1h-dev/amphtml,sklobovskaya/amphtml,wjfang/amphtml,mkhatib/amphtml,Mixpo/amphtml,zhouyx/amphtml,mhc-gh/amphtml,adup-tech/amphtml,smartadserver/amphtml,widespace-os/amphtml,AaronCritchley/amphtml,prateekbh/amphtml,adiant/amphtml,jlucero-contentad/amphtml,shawnbuso/amphtml,adtechnology/amphtml,ampproject/amphtml,BenDz/amphtml-atinternet,amoad-amoe/amphtml,mlb7687/amphtml,smartadserver/amphtml,media-net/amphtml,cvializ/amphtml,adtechnology/amphtml,amoad-amoe/amphtml,tdrl/amphtml,shawnbuso/amphtml,tdrl/amphtml,sortable/amphtml,jridgewell/amphtml,ruturajv-media-net/amphtml,shawnbuso/amphtml,Gregable/amphtml,NataliaLKB/amphtml,jmadler/amphtml,yevheniiminin/amphtml,interspacejp/amphtml,danielrozenberg/amphtml,cvializ/amphtml,yieldmo/amphtml,engtat/amphtml,mhc-gh/amphtml,Mobusi-ads/amphtml,rifler/amphtml,chaveznvg/amphtml,mkhatib/amphtml,yieldmo/amphtml,arealit/amphtml,bpaduch/amphtml,dotandads/amphtml,kmh287/amphtml,sebastianbenz/amphtml,AaronCritchley/amphtml,rlugojr/amphtml,galeksic/amphtml,DarXector/amphtml,tdrl/amphtml,honeybadgerdontcare/amphtml,prateekbh/amphtml,vmarteev/amphtml,avimehta/amphtml,jmadler/amphtml,tlong2/amphtml,adup-tech/amphtml,spotxchange/amphtml,BrightcoveOS/amphtml,pietergreyling/amphtml,jmadler/amphtml,rajkumarsrk/amphtml,BenDz/amphtml,BrightcoveOS/amphtml,criteo-forks/amphtml,yieldmo/amphtml,DAC-f1h-dev/amphtml,gumgum/amphtml,pietergreyling/amphtml,keithwrightbos/amphtml,danielrozenberg/amphtml,Adtoma/amphtml,rsimha-amp/amphtml,BrightcoveOS/amphtml,wjfang/amphtml,keithwrightbos/amphtml,BrightcoveOS/amphtml,honeybadgerdontcare/amphtml,ecoron/amphtml,cory-work/amphtml,kamtschatka/amphtml,dvoytenko/amphtml,rlugojr/amphtml,spotxchange/amphtml,wjfang/amphtml,dvoytenko/amphtml,JuliusThms/amphtml,src-code/amphtml,jasti/amphtml,DarXector/amphtml,taboola/amphtml,adtechnology/amphtml,prateekbh/amphtml,britice/amphtml,alanorozco/amphtml,shawnbuso/amphtml,kixer-com/amphtml,Lith/amphtml,triplelift/amphtml,dotandads/amphtml,tdrl/amphtml,fullspeed-sp/amphtml,devjsun/amphtml,AaronCritchley/amphtml,vmarteev/amphtml,yieldmo/amphtml,prateekbh/amphtml,donttrustthisbot/amphtml,Adtoma/amphtml,Mobusi-ads/amphtml,ColombiaAnalytics/amphtml,ColombiaAnalytics/amphtml,danielrozenberg/amphtml,smartadserver/amphtml,mlb7687/amphtml,taboola/amphtml,jdelhommeau/amphtml,jridgewell/amphtml,danielrozenberg/amphtml,prateekbh/amphtml,luciancrasovan/amphtml,tlong2/amphtml,nekodo/amphtml,dotandads/amphtml,DarXector/amphtml,cory-work/amphtml,Lith/amphtml,rlugojr/amphtml,cory-work/amphtml,jpettitt/amphtml,yandex-pcode/amphtml,gumgum/amphtml,BenDz/amphtml,mkhatib/amphtml,amoad-amoe/amphtml,zhouyx/amphtml,kixer-com/amphtml,kmh287/amphtml,ericlindley-g/amphtml,interspacejp/amphtml,adup-tech/amphtml,media-net/amphtml,kamtschatka/amphtml,jridgewell/amphtml,sebastianbenz/amphtml,voyagegroup/amphtml,yevheniiminin/amphtml,kixer-com/amphtml,Lith/amphtml,keithwrightbos/amphtml,ericlindley-g/amphtml,yieldmo/amphtml,ecoron/amphtml,voyagegroup/amphtml,avimehta/amphtml,yevheni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gegroup/amphtml,jridgewell/amphtml,cvializ/amphtml,galeksic/amphtml,DistroScale/amphtml,dotandads/amphtml,clawr/amphtml,camelburrito/amphtml,aghassemi/amphtml,powdercloud/amphtml,nekodo/amphtml,spotxchange/amphtml,ADITION/amphtml,voyagegroup/amphtml,Gregable/amphtml,alanorozco/amphtml,yandex-pcode/amphtml,yieldbot/amphtml,media-net/amphtml,erwinmombay/amphtml,Gregable/amphtml,ecoron/amphtml,zhangsu/amphtml,pedjoni8/amphtml,jlucero-contentad/amphtml,sharethrough/amphtml,burtcorp/amphtml,shawnbuso/amphtml,pedjoni8/amphtml,clawr/amphtml,devjsun/amphtml,devjsun/amphtml,comScore/amphtml,lannka/amphtml,bpaduch/amphtml,fullspeed-sp/amphtml,smartadserver/amphtml,nexxtv/amphtml,alanorozco/amphtml,DAC-f1h-dev/amphtml,laterpay/amphtml,ruturajv-media-net/amphtml,mlb7687/amphtml,DistroScale/amphtml,BenDz/amphtml-atinternet,media-net/amphtml,britice/amphtml,chaveznvg/amphtml,sklobovskaya/amphtml,ColombiaAnalytics/amphtml,tdrl/amphtml,powdercloud/amphtml,rsimha-amp/amphtml,adup-tech/amphtml,koshka/amphtml,engtat/amphtml,zhangsu/amphtml,pietergreyling/amphtml,zhouyx/amphtml,yieldbot/amphtml,taboola/amphtml,ericlindley-g/amphtml,alanorozco/amphtml,engtat/amphtml,bpaduch/amphtml,gumgum/amphtml,vmarteev/amphtml,laterpay/amphtml,kamtschatka/amphtml,zhangsu/amphtml,kmh287/amphtml,burtcorp/amphtml,yandex-pcode/amphtml,jasti/amphtml,engtat/amphtml,zhucl/amphtml,fullspeed-sp/amphtml,NataliaLKB/amphtml,adiant/amphtml,honeybadgerdontcare/amphtml,fullspeed-sp/amphtml,ampproject/amphtml,devjsun/amphtml,Adtoma/amphtml,cory-work/amphtml,rifler/amphtml,nexxtv/amphtml,bpaduch/amphtml,yevheniiminin/amphtml,engtat/amphtml,avimehta/amphtml,prateekbh/amphtml,arealit/amphtml,bpaduch/amphtml,voyagegroup/amphtml,techhtml/amphtml,triplelift/amphtml,alanorozco/amphtml,jmadler/amphtml,mhc-gh/amphtml,jdelhommeau/amphtml,JuliusThms/amphtml,Adtoma/amphtml,nexxtv/amphtml,jlucero-contentad/amphtml,kamtschatka/amphtml,tlong2/amphtml,danielrozenberg/amphtml,ADITION/amphtml,interspacejp/amphtml,luciancrasovan/amphtml