A function that is called to serialize the content of a text buffer.
It must return the serialized form of the content.
the TextBuffer for which the format is registered
the TextBuffer to serialize
start of the block of text to serialize
end of the block of text to serialize
Return location for the length of the serialized data
user data that was specified when registering the format
a newly-allocated array of guint8 which contains the serialized data, or null if an error occurred