MessageAttributeValue  
    class MessageAttributeValue
The user-specified message attribute value. For string data types, the Value attribute has the same restrictions on the content as the message body. For more information, see <a>SendMessage</a>.
Name, type, value and the message body must not be empty or null. All parts of the message attribute, including Name, Type, and Value, are part of the message size restriction (1 MiB or 1,048,576 bytes).
Types
Properties
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                  Not implemented. Reserved for future use.
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                  Binary type attributes can store any binary data, such as compressed data, encrypted data, or images.
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                  Not implemented. Reserved for future use.
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                  Strings are Unicode with UTF-8 binary encoding. For a list of code values, see ASCII Printable Characters.