location to store the retrieved string. The string retrieved must be freed with g_free().
location to store the retrieved attribute list. When you are done with this list, you must unreference it with pango_attr_list_unref().
location to store position of cursor (in characters) within the preedit string.
Retrieve the current preedit string for the input context, and a list of attributes to apply to the string. This string should be displayed inserted at the insertion point.