diff --git a/audio.go b/audio.go
index 9862ace..72b1d0f 100644
--- a/audio.go
+++ b/audio.go
@@ -53,7 +53,7 @@ type Audio struct {
 	// Description:
 	//   Indicates the start delay in seconds for pre-roll, mid-roll, or
 	//   post-roll ad placements. Refer to List 5.12.
-	StartDelay int64 `json:"startdelay,omitempty"`
+	StartDelay *int64 `json:"startdelay,omitempty"`
 
 	// Attribute:
 	//   sequence
@@ -167,7 +167,7 @@ type Audio struct {
 	//   integer
 	// Description:
 	//   Volume normalization mode. Refer to List 5.17.
-	NVol int8 `json:"nvol,omitempty"`
+	NVol *int8 `json:"nvol,omitempty"`
 
 	// Attribute:
 	//   ext
diff --git a/banner.go b/banner.go
index 8212762..3f5aa74 100644
--- a/banner.go
+++ b/banner.go
@@ -100,7 +100,7 @@ type Banner struct {
 	//   integer
 	// Description:
 	//   Ad position on screen. Refer to List 5.4.
-	Pos int8 `json:"pos,omitempty"`
+	Pos *int8 `json:"pos,omitempty"`
 
 	// Attribute:
 	//   mimes
diff --git a/content.go b/content.go
index 5c39a21..8b768d1 100644
--- a/content.go
+++ b/content.go
@@ -120,7 +120,7 @@ type Content struct {
 	//   integer
 	// Description:
 	//   Production quality. Refer to List 5.13
-	ProdQ int8 `json:"prodq,omitempty"`
+	ProdQ *int8 `json:"prodq,omitempty"`
 
 	// Attribute:
 	//   videoquality
diff --git a/device.go b/device.go
index 1c66688..35f5c83 100644
--- a/device.go
+++ b/device.go
@@ -209,7 +209,7 @@ type Device struct {
 	//   integer
 	// Description:
 	//   Network connection type. Refer to List 5.22.
-	Connectiontype int8 `json:"connectiontype,omitempty"`
+	Connectiontype *int8 `json:"connectiontype,omitempty"`
 
 	// Attribute:
 	//   ifa
diff --git a/enums.go b/enums.go
new file mode 100644
index 0000000..856f7b4
--- /dev/null
+++ b/enums.go
@@ -0,0 +1,282 @@
+package openrtb
+
+//enums and constants for tables 5.x.x (except 5.1 - IAB categories)
+
+//5.2 Banner Ad Types
+
+const (
+	eBannerAdTypeXHTMLTextAd int8 = iota + 1
+	eBannerAdTypeXHTMLBannerAd
+	eBannerAdTypeJavaScriptAd
+	eBannerAdTypeIframe
+)
+
+//5.3 Creative Attributes
+
+const (
+	eCreativeAttributesAudioAdAutoPlay int8 = iota + 1
+	eCreativeAttributesAudioAdUserInitiated
+	eCreativeAttributesExpandableAutomatic
+	eCreativeAttributesExpandableClick
+	eCreativeAttributesExpandableRollover
+	eCreativeAttributesInBannerVideoAdAutoPlay
+	eCreativeAttributesInBannerVideoAdUserInitiated
+	eCreativeAttributesPop
+	eCreativeAttributesProvocative
+	eCreativeAttributesShaky
+	eCreativeAttributesSurveys
+	eCreativeAttributesTextOnly
+	eCreativeAttributesUserInteractive
+	eCreativeAttributesWindowsDialog
+	eCreativeAttributesHasAudioOnOffButton
+	eCreativeAttributesAdProvidesSkipButton
+	eCreativeAttributesAdobeFlash
+)
+
+//5.4 Ad Position
+
+const (
+	eAdPositionUnknown int8 = iota
+	eAdPositionAboveTheFold
+	eAdPositionDepricated
+	eAdPositionBelowTheFold
+	eAdPositionHeader
+	eAdPositionFooter
+	eAdPositionSidebar
+	eAdPositionFullScreen
+)
+
+//5.5 Expandable Direction
+
+const (
+	eExpandableDirectionLeft int8 = iota + 1
+	eExpandableDirectionRight
+	eExpandableDirectionUp
+	eExpandableDirectionDown
+	eExpandableDirectionFullScreen
+)
+
+//5.6 API Frameworks
+
+const (
+	eAPIFrameworksVPAID1 int8 = iota + 1
+	eAPIFrameworksVPAID2
+	eAPIFrameworksMRAID1
+	eAPIFrameworksORMMA
+	eAPIFrameworksMRAID2
+	eAPIFrameworksMRAID3
+)
+
+//5.7 Video Linearity
+
+const (
+	eVideoLinearityLinear int8 = iota + 1
+	eVideoLinearityNonLinear
+)
+
+//5.8 Protocols
+
+const (
+	eProtocolsVAST1 int8 = iota + 1
+	eProtocolsVAST2
+	eProtocolsVAST3
+	eProtocolsVAST1Wrapper
+	eProtocolsVAST2Wrapper
+	eProtocolsVAST3Wrapper
+	eProtocolsVAST4
+	eProtocolsVAST4Wrapper
+	eProtocolsDAAST1
+	eProtocolsDAAST1Wrapper
+)
+
+//5.9 Video Placement Types
+
+const (
+	eVideoPlacementTypesInStream int8 = iota + 1
+	eVideoPlacementTypesInBanner
+	eVideoPlacementTypesInArticle
+	eVideoPlacementTypesInFeed
+	eVideoPlacementTypesInterstitialSliderFloating
+)
+
+//5.10 Playback Methods
+
+const (
+	ePlaybackMethodsInitiatesOnPageLoadWithSoundOn int8 = iota + 1
+	ePlaybackMethodsInitiatesOnPageLoadWithSoundOff
+	ePlaybackMethodsInitiatesOnClickWithSoundOn
+	ePlaybackMethodsInitiatesOnMouseOverWithSoundOn
+	ePlaybackMethodsInitiatesOnEnteringViewportWithSoundOn
+	ePlaybackMethodsInitiatesOnEnteringViewportWithSoundOff
+)
+
+//5.11 Playback Cessation Modes
+
+const (
+	ePlaybackCessationModesOnVideoCompletion int8 = iota + 1
+	ePlaybackCessationModesOnLeavingViewport
+	ePlaybackCessationModesOnLeavingViewportContinuesAsFloatingSlider
+)
+
+//5.12 Start Delay
+
+const (
+	eStartDelayGenericPostRoll int8 = iota - 2
+	eStartDelayGenericMidRoll
+	eStartDelayPreRoll
+)
+
+//5.13 Production Quality
+
+const (
+	eProductionQualityUnknown int8 = iota
+	eProductionQualityProfessionallyProduced
+	eProductionQualityProsumer
+	eProductionQualityUserGenerated
+)
+
+//5.14 Companion Types
+
+const (
+	eCompanionTypesStaticResource int8 = iota + 1
+	eCompanionTypesHTMLResource
+	eCompanionTypesIframeResource
+)
+
+//5.15 Content Delivery Methods
+
+const (
+	eContentDeliveryMethodsStreaming int8 = iota + 1
+	eContentDeliveryMethodsProgressive
+	eContentDeliveryMethodsDownload
+)
+
+//5.16 Feed Types
+
+const (
+	eFeedTypesMusicService int8 = iota + 1
+	eFeedTypesFMAMBroadcast
+	eFeedTypesPodcast
+)
+
+//5.17 Volume Normalization Modes
+
+const (
+	eVolumeNormalizationModesNone int8 = iota
+	eVolumeNormalizationModesAdVolumeAverageNormalizedToContent
+	eVolumeNormalizationModesAdVolumePeakNormalizedToContent
+	eVolumeNormalizationModesAdLoudnessNormalizedToContent
+	eVolumeNormalizationModesCustomVolumeNormalization
+)
+
+//5.18 Content Context
+
+const (
+	eContentContextVideo int8 = iota + 1
+	eContentContextGame
+	eContentContextMusic
+	eContentContextApplication
+	eContentContextText
+	eContentContextOther
+	eContentContextUnknown
+)
+
+//5.19 IQG Media Ratings
+
+const (
+	eIQGMediaRatingsAllAudiences int8 = iota + 1
+	eIQGMediaRatingsEveryoneOver12
+	eIQGMediaRatingsMatureAudiences
+)
+
+//5.20 Location Type
+
+const (
+	eLocationTypeGPS int8 = iota + 1
+	eLocationTypeIP
+	eLocationTypeUser
+)
+
+//5.21 Device Type
+
+const (
+	eDeviceTypeMobileTablet int8 = iota + 1
+	eDeviceTypePersonalComputer
+	eDeviceTypeConnectedTV
+	eDeviceTypePhone
+	eDeviceTypeTablet
+	eDeviceTypeConnectedDevice
+	eDeviceTypeSetTopBox
+)
+
+//5.22 Connection Type
+
+const (
+	eConnectionTypeUnknown int8 = iota
+	eConnectionTypeEthernet
+	eConnectionTypeWIFI
+	eConnectionTypeCellularNetworkUnknownGeneration
+	eConnectionTypeCellularNetwork2G
+	eConnectionTypeCellularNetwork3G
+	eConnectionTypeCellularNetwork4G
+)
+
+//5.23 IP Location Services
+
+const (
+	eIPLocationServiceIP2Location int8 = iota + 1
+	eIPLocationServiceNeustar
+	IPLocationServiceMaxMind
+	IPLocationServiceNetAcuity
+)
+
+//5.24 No-Bid Reason Codes
+
+const (
+	eNoBidReasonUnknownError int8 = iota
+	eNoBidReasonCodeTechnicalError
+	eNoBidReasonCodeInvalidRequest
+	eNoBidReasonCodeKnownWebSpider
+	eNoBidReasonCodeSuspectedNonHumanTraffic
+	eNoBidReasonCodeCloudDataCenterProxyIP
+	eNoBidReasonCodeUnsupportedDevice
+	eNoBidReasonCodeBlockedPublisherOrSite
+	eNoBidReasonCodeUnmatchedUser
+	eNoBidReasonCodeDailyReaderCapMet
+	eNoBidReasonCodeDailyDomainCapMet
+)
+
+//5.25 Loss Reason Codes
+
+const (
+	eLossReasonCodesBidWon int8 = iota
+	eLossReasonCodesInternalError
+	eLossReasonCodesImpressionOpportunityExpired
+	eLossReasonCodesInvalidBidResponse
+	eLossReasonCodesInvalidDealID
+	eLossReasonCodesInvalidAuctionID
+	eLossReasonCodesInvalidAdvertiserDomain
+	eLossReasonCodesMissingMarkup
+	eLossReasonCodesMissingCreativeID
+	eLossReasonCodesMissingBidPrice
+	eLossReasonCodesMissingMinimumCreativeApprovalData
+	eLossReasonCodesBidWasBelowAuctionFloor int8 = iota + 100
+	eLossReasonCodesBidWasBelowDealFloor
+	eLossReasonCodesLostToHigherBid
+	eLossReasonCodesLostToABidForPMPDeal
+	eLossReasonCodesBuyerSeatBlocked
+	eLossReasonCodesCreativeFilteredGeneral uint8 = iota + 200
+	eLossReasonCodesCreativeFilteredPendingProcessingByExchange
+	eLossReasonCodesCreativeFilteredDisapprovedByExchange
+	eLossReasonCodesCreativeFilteredSizeNotAllowed
+	eLossReasonCodesCreativeFilteredIncorrectCreativeFormat
+	eLossReasonCodesCreativeFilteredAdvertiserExclusions
+	eLossReasonCodesCreativeFilteredAppBundleExclusions
+	eLossReasonCodesCreativeFilteredNotSecure
+	eLossReasonCodesCreativeFilteredLanguageExclusions
+	eLossReasonCodesCreativeFilteredCategoryExclusions
+	eLossReasonCodesCreativeFilteredCreativeAttributeExclusions
+	eLossReasonCodesCreativeFilteredAdTypeExclusions
+	eLossReasonCodesCreativeFilteredAnimationTooLong
+	eLossReasonCodesCreativeFilteredNotAllowedInPMPDeal
+)
diff --git a/video.go b/video.go
index a9512a1..3a11347 100644
--- a/video.go
+++ b/video.go
@@ -84,7 +84,7 @@ type Video struct {
 	//   Indicates the start delay in seconds for pre-roll, mid-roll, or
 	//   post-roll ad placements. Refer to List 5.12 for additional
 	//   generic values.
-	StartDelay int64 `json:"startdelay,omitempty"`
+	StartDelay *int64 `json:"startdelay,omitempty"`
 
 	// Attribute:
 	//   placement
@@ -224,7 +224,7 @@ type Video struct {
 	//   integer
 	// Description:
 	//   Ad position on screen. Refer to List 5.4.
-	Pos int8 `json:"pos,omitempty"`
+	Pos *int8 `json:"pos,omitempty"`
 
 	// Attribute:
 	//   companionad