Asks the widget that the input context is attached to to delete characters around the cursor position by emitting the GtkIMContext::delete_surrounding signal. Note that @offset and @n_chars are in characters not in bytes which differs from the usage other places in. In order to use this function, you should first call gtk_im_context_get_surrounding() to get the current context, and call this function immediately afterwards to make sure that you know what you are deleting. You should also account for the fact that even if the signal was handled, the input context might not have deleted all the characters that were requested to be deleted. This function is used by an input method that wants to make subsitutions in the existing text in response to new input. It is not useful for applications.