canInsert
Considering the default editability of the buffer, and tags that affect editability, determines whether text inserted at @iter would be editable.
If text inserted at @iter would be editable then the user should be allowed to insert text at @iter. method@Gtk.TextBuffer.insert_interactive uses this function to decide whether insertions are allowed at a given position.
Return
whether text inserted at @iter would be editable
Parameters
defaultEditability
true if text is editable by default