Document how to use unicode in XTerm and URxvt, reorganise

doc/Language/unicode_entry.pod6

@@ -2,7 +2,7 @@
 
 =TITLE Entering unicode characters
 
-=SUBTITLE Input methods for unicode characters in editors and the shell
+=SUBTITLE Input methods for unicode characters in terminals, the shell, and editors
 
 Perl 6 allows the use of unicode characters as variable names.  Many
 operators are defined with unicode symbols (in particular the L<set/bag
@@ -95,7 +95,71 @@ Sequences can be viewed by right clicking the tray icon and selecting C<Show Seq
 If you wish to add your own sequences, you can do so by either adding/modifying
 C<.XCompose> in C<%USERPROFILE%>, or editing user-defined sequences in the options menu.
 
-=head1 Editors and shells
+=head1 Terminals, shells, and editors:
+
+=head2 XTerm
+
+Unicode support is enabled in XTerm primarily by setting its C<utf8> and
+C<utf8Fonts> options to C<1>, along with its C<locale> option to C<UTF-8>, in
+C<~/.Xdefaults>. Here is a sample configuration that supports displaying enough
+of unicode to program in Perl 6:
+
+    =begin code :lang<.Xdefaults>
+    XTerm*combiningChars:     0
+    XTerm*faceName:           xft:Noto Mono:style=Regular
+    XTerm*faceNameDoublesize: xft:Noto Emoji:style=Regular
+    XTerm*faceSize:           10
+    XTerm*locale:             UTF-8
+    XTerm*titleModes:         16
+    XTerm*useClipping:        false
+    XTerm*utf8                1
+    XTerm*utf8Fonts           1
+    XTerm*utf8Title:          true
+    =end code
+
+=head2 URxvt
+
+Similarly to xterm, unicode support is enabled in URxvt primarily by setting
+its C<locale> option to C<en_US.UTF-8> in C<~/.Xdefaults>. Here is a sample
+configuration that supports displaying enough of unicode to program in Perl 6:
+
+    =begin code :lang<.Xdefaults>
+    URxvt*font:              xft:Noto Mono:pixelsize=14:style=Regular,\
+                             xft:Noto Emoji:pixelsize=14:style=Regular
+    URxvt*letterspace:       -1
+    URxvt*locale:            en_US.UTF-8
+    URxvt*skipBuiltInGlyphs: true
+    =end code
+
+=head2 Unix shell
+
+At the bash shell, one enters unicode characters by using entering
+C<Ctrl-Shift-u>, then the unicode code point value followed by enter.  For
+instance, to enter the character for the element-of operator (∈) use the
+following key combination (whitespace has been added for clarity):
+
+    =begin code :lang<shell>
+    Ctrl-Shift-u 2208 Enter
+    =end code
+
+This also the method one would use to enter unicode characters into the
+C<perl6> REPL, if one has started the REPL inside a Unix shell.
+
+=head2 Screen
+
+L<GNU Screen|https://www.gnu.org/software/screen/> does sport a B<digraph>
+command but with a rather limited digraph table. Thanks to B<bindkey> and
+B<exec> an external program can be used to insert characters to the current
+screen window.
+
+    =begin code :lang<screen>
+    bindkey ^K exec .! digraphs
+    =end code
+
+This will bind control-k to the shell command digraphs. You can use
+L<digraphs|https://github.com/gfldex/digraphs> if you prefer a Perl 6 friendly
+digraph table over L<RFC 1345|https://tools.ietf.org/html/rfc1345> or change it
+to your needs.
 
 =head2 Vim
 X<|Vim>
@@ -184,36 +248,6 @@ run the C<describe-input-method> command:
     C-h I TeX
     =end code
 
-=head2 Unix shell
-
-At the bash shell, one enters unicode characters by using entering
-C<Ctrl-Shift-u>, then the unicode code point value followed by enter.  For
-instance, to enter the character for the element-of operator (∈) use the
-following key combination (whitespace has been added for clarity):
-
-    =begin code :lang<shell>
-    Ctrl-Shift-u 2208 Enter
-    =end code
-
-This also the method one would use to enter unicode characters into the
-C<perl6> REPL, if one has started the REPL inside a Unix shell.
-
-=head2 Screen
-
-L<GNU Screen|https://www.gnu.org/software/screen/> does sport a B<digraph>
-command but with a rather limited digraph table. Thanks to B<bindkey> and
-B<exec> an external program can be used to insert characters to the current
-screen window.
-
-    =begin code :lang<screen>
-    bindkey ^K exec .! digraphs
-    =end code
-
-This will bind control-k to the shell command digraphs. You can use
-L<digraphs|https://github.com/gfldex/digraphs> if you prefer a Perl 6 friendly
-digraph table over L<RFC 1345|https://tools.ietf.org/html/rfc1345> or change it
-to your needs.
-
 =head1 Some characters useful in Perl 6
 
 =head2 L<Smart quotes|https://en.wikipedia.org/wiki/Quotation_mark#Curved_quotes_and_Unicode>