Modifies orig to cover only the text after split_index, and
returns a new item that covers the text before split_index that
used to be in orig. You can think of split_index as the length of
the returned item. split_index may not be 0, and it may not be
greater than or equal to the length of orig (that is, there must
be at least one byte assigned to each item, you can't create a
zero-length item). split_offset is the length of the first item in
chars, and must be provided because the text used to generate the
item isn't available, so pango_item_split() can't count the char
length of the split items itself.
Modifies orig to cover only the text after split_index, and returns a new item that covers the text before split_index that used to be in orig. You can think of split_index as the length of the returned item. split_index may not be 0, and it may not be greater than or equal to the length of orig (that is, there must be at least one byte assigned to each item, you can't create a zero-length item). split_offset is the length of the first item in chars, and must be provided because the text used to generate the item isn't available, so pango_item_split() can't count the char length of the split items itself.