Streams in CLIM also support extended input and output protocols. The extended input stream protocol handles issues pertaining to, in part, non-character input such as mouse clicks. The extended output stream protocol addresses advanced issues such as text cursors, margins, text styles, inter-line spacing, and output recording .
Output recording is a facility CLIM offers for capturing all output done to an extended stream. This information is stored in structures called output records. Output recording is used in the implementation of scrollable windows and incremental redisplay. See Chapter 14, Output Recording and Redisplay and Chapter 15, Extended Stream Input Facilities for more details.
Common Lisp Interface Manager 2.0 User's Guide - 3 Mar 2015