Reword docs about fallbacks on headless linux.

anntzer · anntzer · commit a8bc53a77aaa · 2021-07-18T18:49:17.000+02:00
$DISPLAY (or $WAYLAND_DISPLAY) is not the only thing we consider; we
also check that one can indeed connect to the display server.  (But
there's no point of writing a full explanation of the Linux display
protocols; there's much better docs for that elsewhere online.)
diff --git a/doc/faq/environment_variables_faq.rst b/doc/faq/environment_variables_faq.rst
@@ -7,14 +7,6 @@ Environment variables
 .. contents::
    :backlinks: none
 
-
-.. envvar:: DISPLAY
-
-  The server and screen on which to place windows. This is interpreted by GUI
-  toolkits in a backend-specific manner, but generally refers to an `X.org
-  display name
-  <https://www.x.org/releases/X11R7.7/doc/man/man7/X.7.xhtml#heading5>`_.
-
 .. envvar:: HOME
 
   The user's home directory. On Linux, :envvar:`~ <HOME>` is shorthand for :envvar:`HOME`.
diff --git a/tutorials/introductory/usage.py b/tutorials/introductory/usage.py
@@ -299,11 +299,10 @@ def my_plotter(ax, data1, data2, param_dict):
 #
 # Without a backend explicitly set, Matplotlib automatically detects a usable
 # backend based on what is available on your system and on whether a GUI event
-# loop is already running. On Linux, if the environment variable
-# :envvar:`DISPLAY` is unset, the "event loop" is identified as "headless",
-# which causes a fallback to a noninteractive backend (agg); in all other
-# cases, an interactive backend is preferred (usually, at least tkagg will be
-# available).
+# loop is already running.  An interactive backend is usually preferred (at
+# least tkagg should be available); as an exception, on Linux, if Matplotlib
+# cannot connect to either an X display or a Wayland display, the system is
+# considered "headless" and a noninteractive backend (agg) is used.
 #
 # Here is a detailed description of the configuration methods:
 #

Original file line number	Diff line number	Diff line change
`@@ -299,11 +299,10 @@ def my_plotter(ax, data1, data2, param_dict):`
`299`	`299`	`#`
`300`	`300`	`# Without a backend explicitly set, Matplotlib automatically detects a usable`
`301`	`301`	`# backend based on what is available on your system and on whether a GUI event`
`302`		`-# loop is already running. On Linux, if the environment variable`
`303`		-# :envvar:`DISPLAY` is unset, the "event loop" is identified as "headless",
`304`		`-# which causes a fallback to a noninteractive backend (agg); in all other`
`305`		`-# cases, an interactive backend is preferred (usually, at least tkagg will be`
`306`		`-# available).`
	`302`	`+# loop is already running. An interactive backend is usually preferred (at`
	`303`	`+# least tkagg should be available); as an exception, on Linux, if Matplotlib`
	`304`	`+# cannot connect to either an X display or a Wayland display, the system is`
	`305`	`+# considered "headless" and a noninteractive backend (agg) is used.`
`307`	`306`	`#`
`308`	`307`	`# Here is a detailed description of the configuration methods:`
`309`	`308`	`#`