diff --git a/Doc/library/idle.rst b/Doc/library/idle.rst
index 2b9bd4b..6ef1565 100644
--- a/Doc/library/idle.rst
+++ b/Doc/library/idle.rst
@@ -670,8 +670,16 @@
 code execution process.  A connection must be established whenever the Shell
 starts or restarts.  (The latter is indicated by a divider line that says
 'RESTART'). If the user process fails to connect to the GUI process, it
-displays a ``Tk`` error box with a 'cannot connect' message that directs the
-user here.  It then exits.
+usually displays a ``Tk`` error box with a 'cannot connect' message
+that directs the user here.  It then exits.
+
+One specific connection failure on Unix systems results from
+misconfigured masquerading rules somewhere in a system's network setup.
+When IDLE is started from a terminal, one will see a message starting
+with ``** Invalid host:``.
+The valid value is ``127.0.0.1 (idlelib.rpc.LOCALHOST)``.
+One can diagnose with ``tcpconnect -irv 127.0.0.1 6543`` in one
+terminal window and ``tcplisten <same args>`` in another.
 
 A common cause of failure is a user-written file with the same name as a
 standard library module, such as *random.py* and *tkinter.py*. When such a
@@ -709,6 +717,13 @@
 starting it from a console or terminal (``python -m idlelib``) and see if
 this results in an error message.
 
+On Unix-based systems with tcl/tk older than ``8.6.11`` (see
+``About IDLE``) certain characters of certain fonts can cause
+a tk failure with a message to the terminal.  This can happen either
+if one starts IDLE to edit a file with such a character or later
+when entering such a character.  If one cannot upgrade tcl/tk,
+then re-configure IDLE to use a font that works better.
+
 Running user code
 ^^^^^^^^^^^^^^^^^
 
diff --git a/Lib/idlelib/help.html b/Lib/idlelib/help.html
index 924042d..e80384b 100644
--- a/Lib/idlelib/help.html
+++ b/Lib/idlelib/help.html
@@ -5,7 +5,7 @@
   <head>
     <meta charset="utf-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
-    <title>IDLE &#8212; Python 3.10.0a5 documentation</title>
+    <title>IDLE &#8212; Python 3.10.0a6 documentation</title>
     <link rel="stylesheet" href="../_static/pydoctheme.css" type="text/css" />
     <link rel="stylesheet" href="../_static/pygments.css" type="text/css" />
 
@@ -18,7 +18,7 @@
     <script src="../_static/sidebar.js"></script>
 
     <link rel="search" type="application/opensearchdescription+xml"
-          title="Search within Python 3.10.0a5 documentation"
+          title="Search within Python 3.10.0a6 documentation"
           href="../_static/opensearch.xml"/>
     <link rel="author" title="About these documents" href="../about.html" />
     <link rel="index" title="Index" href="../genindex.html" />
@@ -71,7 +71,7 @@
 
 
     <li id="cpython-language-and-version">
-      <a href="../index.html">3.10.0a5 Documentation</a> &#187;
+      <a href="../index.html">3.10.0a6 Documentation</a> &#187;
     </li>
 
           <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> &#187;</li>
@@ -632,8 +632,15 @@
 code execution process.  A connection must be established whenever the Shell
 starts or restarts.  (The latter is indicated by a divider line that says
 ‘RESTART’). If the user process fails to connect to the GUI process, it
-displays a <code class="docutils literal notranslate"><span class="pre">Tk</span></code> error box with a ‘cannot connect’ message that directs the
-user here.  It then exits.</p>
+usually displays a <code class="docutils literal notranslate"><span class="pre">Tk</span></code> error box with a ‘cannot connect’ message
+that directs the user here.  It then exits.</p>
+<p>One specific connection failure on Unix systems results from
+misconfigured masquerading rules somewhere in a system’s network setup.
+When IDLE is started from a terminal, one will see a message starting
+with <code class="docutils literal notranslate"><span class="pre">**</span> <span class="pre">Invalid</span> <span class="pre">host:</span></code>.
+The valid value is <code class="docutils literal notranslate"><span class="pre">127.0.0.1</span> <span class="pre">(idlelib.rpc.LOCALHOST)</span></code>.
+One can diagnose with <code class="docutils literal notranslate"><span class="pre">tcpconnect</span> <span class="pre">-irv</span> <span class="pre">127.0.0.1</span> <span class="pre">6543</span></code> in one
+terminal window and <code class="docutils literal notranslate"><span class="pre">tcplisten</span> <span class="pre">&lt;same</span> <span class="pre">args&gt;</span></code> in another.</p>
 <p>A common cause of failure is a user-written file with the same name as a
 standard library module, such as <em>random.py</em> and <em>tkinter.py</em>. When such a
 file is located in the same directory as a file that is about to be run,
@@ -664,6 +671,12 @@
 <p>If IDLE quits with no message, and it was not started from a console, try
 starting it from a console or terminal (<code class="docutils literal notranslate"><span class="pre">python</span> <span class="pre">-m</span> <span class="pre">idlelib</span></code>) and see if
 this results in an error message.</p>
+<p>On Unix-based systems with tcl/tk older than <code class="docutils literal notranslate"><span class="pre">8.6.11</span></code> (see
+<code class="docutils literal notranslate"><span class="pre">About</span> <span class="pre">IDLE</span></code>) certain characters of certain fonts can cause
+a tk failure with a message to the terminal.  This can happen either
+if one starts IDLE to edit a file with such a character or later
+when entering such a character.  If one cannot upgrade tcl/tk,
+then re-configure IDLE to use a font that works better.</p>
 </div>
 <div class="section" id="running-user-code">
 <h3>Running user code<a class="headerlink" href="#running-user-code" title="Permalink to this headline">¶</a></h3>
@@ -958,7 +971,7 @@
 
 
     <li id="cpython-language-and-version">
-      <a href="../index.html">3.10.0a5 Documentation</a> &#187;
+      <a href="../index.html">3.10.0a6 Documentation</a> &#187;
     </li>
 
           <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> &#187;</li>
@@ -990,7 +1003,7 @@
 <br />
     <br />
 
-    Last updated on Feb 23, 2021.
+    Last updated on Mar 29, 2021.
     <a href="https://docs.python.org/3/bugs.html">Found a bug</a>?
     <br />
 
diff --git a/Misc/NEWS.d/next/IDLE/2021-03-29-16-22-27.bpo-42225.iIeiLg.rst b/Misc/NEWS.d/next/IDLE/2021-03-29-16-22-27.bpo-42225.iIeiLg.rst
new file mode 100644
index 0000000..59fb08b
--- /dev/null
+++ b/Misc/NEWS.d/next/IDLE/2021-03-29-16-22-27.bpo-42225.iIeiLg.rst
@@ -0,0 +1,2 @@
+Document that IDLE can fail on Unix either from misconfigured IP masquerage
+rules or failure displaying complex colored (non-ascii) characters.