Like insert, but the insertion will not occur if
iter is at a
non-editable location in the buffer.
Usually you want to prevent insertions at ineditable locations if the insertion results from a user action (is interactive).
default_editable indicates the editability of text that doesn't have a tag affecting editability applied to it. Typically the
result of get_editable is appropriate here.
a position in this
some UTF-8 text
length of text in bytes, or -1
default editability of buffer
whether text was actually inserted