Copies items into the clipboard.
The system may execute a copy (in response to other method calls) without calling this method. To extend or re-implement copying, override the do-copy in text% or do-copy in pasteboard% method of an editor.
Copies the selected items into the clipboard. If extend? is not #f, the old clipboard contents are appended.
See Cut and Paste for a discussion of the time argument. If time is outside the platform-specific range of times, an exn:application:mismatch exception is raised.