# Constants
Accept header.
AcceptCharset Accept-Charset header.
AcceptEncoding header.
AcceptLanguage Accept-Language header.
AcceptRanges Accept-Ranges header.
AccessControlAllowCredentials header.
AccessControlAllowHeaders header.
AccessControlAllowMethods header.
AccessControlAllowOrigin header.
AccessControlExposeHeaders header.
AccessControlMaxAge header.
AccessControlRequestHeaders header.
AccessControlRequestMethod header.
Allow request methods.
Authorization header.
AutoSubmitted Auto-Submitted header.
CacheControl Cache-Control header.
ContentDisposition header.
ContentEncoding header.
ContentLength header.
ContentRange Content-Range header.
ContentType header.
Date header.
DeliveredTo Delivered-To header.
ETag header.
Expires header.
IfMatch If-Match header.
IfModifiedSince header.
IfNoneMatch If-None-Match header.
IfRange If-Range header.
IfUnmodifiedSince If-Unmodified-Since header.
LastModified header.
Location header.
MailImportance Header for mail messages: Importance.
MailMSMailPriority Header for mail messages: X-MSMail-Priority.
MailPriority Header for mail messages: Priority.
MailXPriority Header for mail messages: X-Priority.
MessageID Message-Id header.
MsEchoRequest Ms-Echo-Request header.
Origin header.
Pragma header.
Range Range header.
Received header.
Referer header.
RetryAfter Retry-After header.
ReturnPath Return-Path header.
Upgrade header.
UserAgent User-Agent header.
Vary header.
WWWAuthenticate header.
XCaptchaType X-Captcha-Type header.
XCarrier X-Carrier header.
XConnectionType X-Connection-Type header.
XCoreSDToken The X-Coresd-Token header.
XDayOfWeek X-Day-Of-Week header.
XDeviceManufacturer X-Device-Manufacturer header.
XDeviceModel X-Device-Model header.
XFailedRecipients X-Failed-Recipients header.
XForwardedFor header.
XForwardedProto header.
XGeoCity X-Geo-City header.
XGeoContinent X-Geo-Continent header.
XGeoCountry X-Geo-Country header.
XGeoRegion X-Geo-Region header.
XInternetServiceProvider X-Internet-Service-Provider header.
XProjectID The X-Project-Id header.
XProxyType X-ProxyType header.
XRealIP header.
XRecaptchaSiteKey X-Recaptcha-Site-Key header.
XRedefinitionDeny X-Redefinition-Deny header.
XRegistrationInviteCode X-Registration-Invite-Code header.
XRequestedWith X-Requested-With header.
XScheme header.
XScreenSize X-Screen-Size header.
XTimeZone X-Time-Zone header.
XUserAgent X-User-Agent header.