+* Upgrading from LyX 2.3.x
+
+The format of preference and session files has changed. LyX 2.4.x is able to
+read old files but will save them in the new format.
+
+The format of layout files has changed but, as before, layout2layout.py will
+convert older versions to the new format automatically.
+
+* Upgrading from LyX 2.2.x:
+
+The format of preference and session files has changed. LyX 2.3.x is able to
+read old files but will save them in the new format.
+
+The format of layout files has changed but, as before, layout2layout.py will
+convert older versions to the new format automatically.
+
+The external_templates file has been split into one file per template,
+which are now located in lib/xtemplates/*.xtemplate. This makes it easier
+to add new templates or modify existing ones. If you have modified
+the external_templates file, you will have to move the modifications to
+the respective *.xtemplate file manually.
+
+If using TeX fonts and en- and em-dashes are output as font ligatures,
+when exporting documents containing en- and em-dashes to the format of
+LyX 2.0 or earlier, the following line has to be manually added to the
+unicodesymbols file of that LyX version:<br>
+0x200b "\\hspace{0pt}" "" "" "" "" # ZERO WIDTH SPACE<br>
+This avoids "uncodable character" issues if the document is actually
+loaded by that LyX version. LyX 2.1 and later versions already have the
+necessary definition in their unicodesymbols file.
+
+If trying to compile documents using R scripts and sweave/knitr, LyX
+2.3.x would not allow for re-running the R scripts, unless the user:
+1) explicitly disables the "Forbid use of needauth converters"
+option in the LyX preferences;
+2) provides explicit consent to the use of the converter on the first
+compilation of the R-enhanced document.
+
+* Upgrading from LyX 2.1.x:
+
+The format of preference and session files has changed. LyX 2.2.x is able to
+read old files but will save them in the new format.
+
+The format of layout files has changed but, as before, layout2layout.py will
+convert older versions to the new format automatically.
+
+The prefix for subsections in labels and references has been changed from
+"sub:" to "subsec:" in order to avoid a clash with subfloats (conflicting
+\subref command, see bug #7550). Files are automatically converted to the new
+scheme. Please assure that you adapt external refstyle or prettyref definitions
+and your own layout files.
+
+BibTeX errors are now processed and cause LyX to show the errors dialog.
+Before, these errors were ignored, which means that it may happen that
+documents that compiled without error with a previous version now
+compile with error. However, because now in 2.2.x users can click on
+the "Show Output Anyway" button, the document can still be viewed.
+
+Missing characters in the output are now reported as errors. This leads
+to error reports for documents that compiled without error before.
+However, the error was always present but went undetected!
+
+Documents using Times fonts and containing Greek characters may now fail
+to compile under pdflatex for users of MikTeX due to an automatically
+half-installed "grtimes" package. A workaround in LyX was removed as it
+stands in the way of alternative approaches (see bug #6469).
+
+With LuaTeX, LyX now uses polyglossia instead of babel if the language
+package option "Automatic" is selected. In order to use babel, select
+"Always babel" instead. This may be needed if a document uses code that
+is specific to babel.
+
+* Upgrading from LyX 2.0.x:
+
+Python version >=2.4 is now required.
+
+Python version >3.0 is still not yet supported.
+
+* Upgrading from LyX 1.6.x:
+
+The typeset of your documents with non-english language can slightly
+change in case of math environments and floats. LyX 2.0.x now has its
+own translation machinery for the strings that are not translated by
+babel.
+
+The format of preference and session files has changed. LyX 2.0.x is
+able to read old files but will save them in the new format.
+
+The format of layout files has changed but, as before, layout2layout.py
+will convert older versions to the new format automatically.
+
+The syntax of the languages file has been changed. If you use a
+modified languages file, you will need to adapt it to the new syntax.
+
+There has been a large change in how Flex insets are named.
+When exporting back to 1.6.x format user-defined flex insets will not
+be properly reverted. See RELEASE-NOTES for details.
+
+The UI layout named "classic.ui" and some localized keyboard bindings
+(sv, pt, fi) are not being shipped anymore.
+
+* Upgrading from LyX 1.5.x:
+
+The format of preference and session files has changed. LyX 1.6.x is
+able to read old files but will save them in the new format.
+
+The format of layout files has changed but, as before,
+layout2layout.py will convert older versions to the new format
+automatically.
+
+* Upgrading from LyX 1.4.x:
+
+The biggest change in 1.5 is the switch to Unicode. Please refer to
+the section "Document transfer" below for some things you might take
+into account before upgrading.
+
+The format of the preferences file has changed slightly. LyX 1.5.x is
+able to read old preferences files, but it will save them in the new
+format, so it is not possible to run LyX 1.4.x and 1.5.x with the same
+personal configuration directory. If you are upgrading from 1.4.x and
+do not intend to continue using 1.4.x, you should delete your existing
+preferences file and allow LyX to create a new one.
+
+The list of recently open files is now stored in a different location.
+It will therefore be reset when upgrading from LyX 1.4.x.
+
+The format of the layout files has also changed, but LyX 1.5.x uses a
+converter layout2layout.py written in python that will convert old layout
+files on the fly (see below, section "Document transfer").
+
+* Upgrading from LyX 1.3.x:
+
+The format of the external template file has changed substantially with
+LyX 1.4.0. Automatic conversion is not available, so you need to convert
+your external templates manually. The new format of the external template
+configuration file is described in chapter 6.5 of the Customization Guide.
+
+* Upgrading from LyX 1.2.x:
+
+Since 1.3.0, you have to do the following changes:
+
+One of the perennial bug bears of LyX users in the past has been that
+they have had to run Edit->Reconfigure when starting their new version
+of the code for the first time. Strange and wonderful things would
+often result if they forgot to do this, so LyX 1.3.0 now runs
+Edit->Reconfigure automatically the first time the program is run.