update sigil env vars, fix duplication, add force native

Author: kevinhendricks

src/OEBPS/Text/advanced_topics.xhtml

@@ -42,8 +42,6 @@
 
 <li><p><span class="listheading">SIGIL_FUNCTION_REPLACE_LOGFILE</span> Setting this to the full path (including file name and extension) to a user-writeable location will cause Sigil to output any Python Function Replace log messages to that log file.  Unset this environment after debugging is important as this file will continue to build up output eventually filling up user disk space and slowing down Sigil.</p></li>
 
-  <li><p><span class="listheading">SIGIL_USE_FREETYPE_FONTENGINE</span> This environment variable is <b>Windows Only</b>. Setting this will tell Sigil to use the FreeType Font Engine.  This is useful on Windows for users who make heavy use of // Woff/woff2 fonts in their epub.  Current Qt version of the Windows Font Engine does not support these font types.</p></li>
-
   <li><p><span class="listheading">SIGIL_USE_FREETYPE_FONTENGINE</span> This environment variable is <b>Windows Only</b>. Setting this will tell Sigil to use the FreeType Font Engine.  This is useful on Windows for users who make heavy use of // Woff/woff2 fonts in their epub.  Current Qt version of the Windows Font Engine does not support these font types.</p></li>
 
     <li><p><span class="listheading">SIGIL_PREVIEW_TIMEOUT</span> Setting this to a number (of milliseconds) will determine the length of time after user input stops while editing in CodeView until Preview is updated.  The minimum delay is 1000 milliseconds and the maximum delay can be set up to 10000 milliseconds.  There is typically no reason to set this unless you are editing huge xhtml files that take too long for Preview to update.</p></li>
@@ -61,6 +59,8 @@
     <li><p><span class="listheading">SIGIL_DICTIONARIES</span> This environment Variable is primarily <b>Linux Only</b>. Setting this tells Sigil where to locate the hunspell dictionaries installed on your system.</p></li>
 
     <li><p><span class="listheading">SIGIL_NO_CUSTOM_DIRECTORY_ICONS</span> This environment variable is is useful if you make heavy use of networked drives with lots and lots of files.  It prevents the constant search for system level custom file icons and so it can greatly speed up the performance of non-native file dialogs, like "Add Existing...".</p></li>
+
+ <li><p><span class="listheading">SIGIL_FORCE_NATIVE_FILE_DIALOG</span> This environment variable forces Sigil to use the operating system's native file dialog.  Unfortunately, using native file dialogs has resulted in a number of crashing issues in recent versions of Qt.  Use at your own risk.</p></li>
   </ul>
 
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