+# Initially tested with screen 3.09.08
+#
+# According to its manual page
+#
+# Screen is a full-screen window manager that multiplexes a physical
+# terminal between several processes (typically interactive shells). Each
+# virtual terminal provides the functions of a DEC VT100 terminal and, in
+# addition, several control functions from the ISO 6429 (ECMA 48, ANSI
+# X3.64) and ISO 2022 standards (e.g. insert/delete line and support for
+# multiple character sets).
+#
+# However, there is a design error in its support for video highlights. The
+# program uses a table (rendlist) which equates the SGR codes to terminal
+# capabilities. That, and color-decoding are hardcoded in screen; its behavior
+# is modified only by the presence or absence of the corresponding capabilities.
+# Not by their values.
+#
+# If screen sets the TERMCAP variable, it uses hardcoded strings which
+# correspond to the rendlist table.
+#
+# The table gives this information:
+#
+# SGR capability
+# --- ---------
+# 1 bold
+# 2 dim
+# 3 standout
+# 4 underline
+# 5 blink
+# - (unused 6)
+# 7 reverse
+# - (unused 8-21)
+# 22 reset bold, standout and dim
+# 23 reset standout
+# 24 reset underline
+# 25 reset blink
+# - (unused 26)
+# 27 reset reverse
+#
+# ECMA-48 differs from this: 3 and 23 set and reset italics, respectively.
+# ECMA-48 does not define "standout" - that is a termcap/terminfo abstraction.
+# Without some redesign of screen, it is not possible to extend the set of
+# capabilities. Substitution would be possible, e.g., sending italics in
+# place of underline.
+#
+# Because screen uses hard-coded parsing, it does not check if two capabilities
+# use the same value. For example, changing standout to be the same as any of
+# the other capabilities will confuse screen. Curses applications which use
+# sgr are not impacted (because that usually resets all capabilities before
+# setting any), but termcap applications do not use sgr -TD
projects / ncurses.git / blobdiff