This document uses the following terms:
conversation: A single representation of a send/response series of email messages. A conversation appears in the Inbox as one unit and allows the user to view and read the series of related email messages in a single effort.
conversation ID: A unique value that is associated with a conversation. It is assigned to each Message object that is part of a conversation and it is used to identify the conversation to which the message belongs.
conversation index: A value that specifies the location of a message within a conversation. A client can use this value to identify the parent and child messages of a message, and then generate a tree view of the conversation that contains those messages.
Hypertext Markup Language (HTML): An application of the Standard Generalized Markup Language (SGML) that uses tags to mark elements in a document, as described in [HTML].
message part: A message body with a string property that contains only the portion of an email message that is original to the message. It does not include any previous, quoted messages. If a message does not quote a previous message, the message part is identical to the message body.
recipient information cache: An information store that contains a list of the contacts with whom a user has interacted most often and most recently, and with whom the user is likely to interact again.
Wireless Application Protocol (WAP) Binary XML (WBXML): A compact binary representation of XML that is designed to reduce the transmission size of XML documents over narrowband communication channels.
XML: The Extensible Markup Language, as described in [XML1.0].
XML element: An XML structure that typically consists of a start tag, an end tag, and the information between those tags. Elements can have attributes and can contain other elements.
XML namespace: A collection of names that is used to identify elements, types, and attributes in XML documents identified in a URI reference [RFC3986]. A combination of XML namespace and local name allows XML documents to use elements, types, and attributes that have the same names but come from different sources. For more information, see [XMLNS-2ED].
XML schema: A description of a type of XML document that is typically expressed in terms of constraints on the structure and content of documents of that type, in addition to the basic syntax constraints that are imposed by XML itself. An XML schema provides a view of a document type at a relatively high level of abstraction.
MAY, SHOULD, MUST, SHOULD NOT, MUST NOT: These terms (in all caps) are used as defined in [RFC2119]. All statements of optional behavior use either MAY, SHOULD, or SHOULD NOT.