- 1) Introduction
- 2) Notational Conventions and Generic Grammar
- 3) Protocol Parameters
- 4) HTTP Message
- 5) Request
- 6) Response
- 7) Entity
- 8) Connections
- 9) Method Definitions
- 10) Status Code Definitions
- 1) Informational 1xx
- 2) Successful 2xx
- 3) Redirection 3xx
- 4) Client Error 4xx
- 1) 400 Bad Request
- 2) 401 Unauthorized
- 3) 402 Payment Required
- 4) 403 Forbidden
- 5) 404 Not Found
- 6) 405 Method Not Allowed
- 7) 406 Not Acceptable
- 8) 407 Proxy Authentication Required
- 9) 408 Request Timeout
- 10) 409 Conflict
- 11) 410 Gone
- 12) 411 Length Required
- 13) 412 Precondition Failed
- 14) 413 Request Entity Too Large
- 15) 414 Request-URI Too Long
- 16) 415 Unsupported Media Type
- 17) 416 Requested Range Not Satisfiable
- 18) 417 Expectation Failed
- 5) Server Error 5xx
- 11) Access Authentication
- 12) Content Negotiation
- 13) Caching in HTTP
- 1) ..
- 2) Expiration Model
- 3) Validation Model
- 4) Response Cacheability
- 5) Constructing Responses From Caches
- 6) Caching Negotiated Responses
- 7) Shared and Non-Shared Caches
- 8) Errors or Incomplete Response Cache Behavior
- 9) Side Effects of GET and HEAD
- 10) Invalidation After Updates or Deletions
- 11) Write-Through Mandatory
- 12) Cache Replacement
- 13) History Lists
- 14) Header Field Definitions
- 1) Accept
- 2) Accept-Charset
- 3) Accept-Encoding
- 4) Accept-Language
- 5) Accept-Ranges
- 6) Age
- 7) Allow
- 8) Authorization
- 9) Cache-Control
- 10) Connection
- 11) Content-Encoding
- 12) Content-Language
- 13) Content-Length
- 14) Content-Location
- 15) Content-MD5
- 16) Content-Range
- 17) Content-Type
- 18) Date
- 19) ETag
- 20) Expect
- 21) Expires
- 22) From
- 23) Host
- 24) If-Match
- 25) If-Modified-Since
- 26) If-None-Match
- 27) If-Range
- 28) If-Unmodified-Since
- 29) Last-Modified
- 30) Location
- 31) Max-Forwards
- 32) Pragma
- 33) Proxy-Authenticate
- 34) Proxy-Authorization
- 35) Range
- 36) Referer
- 37) Retry-After
- 38) Server
- 39) TE
- 40) Trailer
- 41) Transfer-Encoding
- 42) Upgrade
- 43) User-Agent
- 44) Vary
- 45) Via
- 46) Warning
- 47) WWW-Authenticate
- 15) Security Considerations
- 16) Acknowledgments
- 17) References
- 18) Authors' Addresses
- 19) Appendices
- 20) Index
- 21) Full Copyright Statement
- 22) Acknowledgement
3.10 Language Tags
A language tag identifies a natural language spoken, written, or otherwise conveyed by human beings for communication of information to other human beings. Computer languages are explicitly excluded. HTTP uses language tags within the Accept-Language and Content- Language fields.
The syntax and registry of HTTP language tags is the same as that defined by RFC 1766 [1]. In summary, a language tag is composed of 1 or more parts: A primary language tag and a possibly empty series of subtags:
language-tag | = primary-tag *( "-" subtag ) |
primary-tag | = 1*8ALPHA |
subtag | = 1*8ALP |
White space is not allowed within the tag and all tags are case- insensitive. The name space of language tags is administered by the IANA. Example tags include: en, en-US, en-cockney, i-cherokee, x-pig-latin where any two-letter primary-tag is an ISO-639 language abbreviation and any two-letter initial subtag is an ISO-3166 country code. (The last three tags above are not registered tags; all but the last are examples of tags which could be registered in future.)