bpo-33000: Document that IDLE's shell has no line limit. (#10373)
A program that runs indefinitely can overfill memory.
diff --git a/Doc/library/idle.rst b/Doc/library/idle.rst
index fa58e2d..f353fbc 100644
--- a/Doc/library/idle.rst
+++ b/Doc/library/idle.rst
@@ -671,15 +671,23 @@
corresponding output device. When IDLE executes user code, ``sys.stdout``
and ``sys.stderr`` are connected to the display area of IDLE's Shell. Some of
its features are inherited from the underlying Tk Text widget. Others
-are programmed additions.
+are programmed additions. Where it matters, Shell is designed for development
+rather than production runs.
+
+For instance, Shell never throws away output. A program that sends unlimited
+output to Shell will eventually fill memory, resulting in a memory error.
+In contrast, some system text windows only keep the last n lines of output.
+A Windows console, for instance, keeps a user-settable 1 to 9999 lines,
+with 300 the default.
Text widgets display a subset of Unicode, the Basic Multilingual Plane (BMP).
Which characters get a proper glyph instead of a replacement box depends on
the operating system and installed fonts. Newline characters cause following
-text to appear on a new line, but other control characters are replaced
-with a box. But note that the ``repr()`` function, which is used for
-interactive echo of expression values, replaces control characters
-with escape codes before they are output.
+text to appear on a new line, but other control characters are either
+replaced with a box or deleted. However, ``repr()``, which is used for
+interactive echo of expression values, replaces control characters,
+some BMP codepoints, and all non-BMP characters with escape codes
+before they are output.
Normal and error output are generally kept separate (on separate lines)
from code input and each other. They each get different highlight colors.