Editing Session Description Protocol (section)

==Attributes==
SDP uses attributes to extend the core protocol. Attributes can appear within the Session or Media sections and are scoped accordingly as ''session-level'' or ''media-level''. New attributes are added to the standard occasionally through registration with IANA.<ref>{{cite web |url=https://www.iana.org/assignments/sdp-parameters |title=Registry of the SDP Parameters |publisher=Internet Assigned Numbers Authority |access-date=2021-01-15}}</ref>

Attributes are either properties or values:
*Property: a=''flag'' conveys a Boolean property of the media or session.
*Value: a=''attribute'':''value'' provides a named parameter.

Two of these attributes are specially defined:
* a=charset:''encoding'' is used in the session or media sections to specify a different character encoding (as registered in the IANA registry<ref>{{cite web| url = https://www.iana.org/assignments/character-sets| title = Registry of the Character Sets Encodings, on the Internet Assigned Numbers Authority site}}</ref>) from the recommended default value (''UTF-8'') for standard protocol keys. These values contain a text that is intended to be displayed to a user.
* a=sdplang:''code'' is used to specify the language of text. Alternate text in multiple languages may be carried in the session, and selected automatically by the user agent according to user preferences.{{clarify|date=March 2021}}
In both cases, text fields intended to be displayed to a user are interpreted as opaque strings, but rendered to the user or application with the values indicated in the last occurrence of the fields ''charset'' and ''sdplang'' in the current media section, or otherwise their last value in the session section.

The parameters ''v'', ''s'', and ''o'' are mandatory, must not be empty, and should be UTF-8-encoded. They are used as identifiers and are not intended to be displayed to users.

A few other attributes are also present in the example, either as a session-level attribute (such as the attribute in property form ''a=recvonly''),<ref group="note">This session-level attribute also applies to the described media unless the value is overridden by a media-level attribute.</ref> or as a media-level attribute (such as the attribute in value form ''a=rtpmap:99 h263-1998/90000'' for the video in the example).