backspace
Performs the appropriate action as if the user hit the delete key with the cursor at the position specified by @iter.
In the normal case a single character will be deleted, but when combining accents are involved, more than one character can be deleted, and when precomposed character and accent combinations are involved, less than one character will be deleted.
Because the buffer is modified, all outstanding iterators become invalid after calling this function; however, the @iter will be re-initialized to point to the location where text was deleted.
Return
true if the buffer was modified
Parameters
iter
a position in @buffer
interactive
whether the deletion is caused by user interaction
defaultEditable
whether the buffer is editable by default