Remove unsupported encoding "pt254".

This encoding (modified Mac Cyrillic for Asian languages) is rarely used and not supported by Gnu iconv.

Update comments in lib/encodings.

Update ctests: Gnu iconv only supports cp858, if configured with "--enable-extra-encodings".

development/autotests/invertedTests

@@ -143,9 +143,6 @@ export/export/latex/unicodesymbols/009-cyrillic_(cp855|cp866|cp1251|koi8-r|koi8-
 export/export/latex/unicodesymbols/069-greek-extended(|_utf8x)_pdf2
 export/export/latex/unicodesymbols/069-greek-extended-textalpha_utf8x_pdf2
 
-#10502 encodings cp858_ and pt254 not supported by iconv
-export/export/latex/cp858_pdf2
-
 
 # ==============================================================
 Sublabel: ert

development/autotests/unreliableTests

@@ -60,6 +60,11 @@ Sublabel: varying_versions
 # Note that a full, up-to-date TeX Live installation is required so this
 # sublabel is about versions of other dependencies.
 
+# Encoding cp858 only supported by some iconv variants
+# Gnu iconv only supports it, if configured with "--enable-extra-encodings"
+# (see https://www.gnu.org/software/libiconv/)
+export/export/latex/cp858_pdf2
+
 
 Sublabel: wrong_output
 ######################

lib/encodings

@@ -17,6 +17,12 @@
 # In this case, TeX control characters in high bytes is not a problem.
 # The invocation is platex -kanji=<LaTeX name>
 
+# The set of "iconv" supported encodings is system dependent.
+
+# For Gnu libiconv, supported encodings are listed at
+# https://www.gnu.org/software/libiconv/
+# and available via the `iconv --list` command.
+
 # Syntax: Encoding <LyX name> <LaTeX name> <GUI name> <iconv name> <width> <package> End
 
 # LyX name:    Name used by the file format and in lib/languages. Must be unique!
@@ -26,8 +32,21 @@
 # width:       One of fixed, variable, or variableunsafe (see above).
 # package:     One of none, inputenc, CJK, or japanese (see above).
 
-# encodings used by inputenc.sty
+# Encodings used with inputenc.sty
+# ================================
 
+# "inputenc" is a base LaTeX package that provides an extensible framework
+# for conversion of a document encoding into an "LaTeX Internal Character
+# Representation" (LICR) and a set of encoding definitions
+# (<LaTeX name>.def files). Additional encoding definitions are provided by
+# several language support packages.
+#
+# The following encodings from http://www.ctan.org/pkg/latex-cyrillic are
+# not included, because they are not widely used and lack iconv support:
+# ctt, dbk, isoir111, koi8-ru, lcyenc, maccyr, macukr, mik, mls, mnk, mos,
+# and pt254.
+
+# inputenc's standard utf8 support:
 Encoding utf8 utf8 "Unicode (utf8)" UTF-8 variable inputenc
 End
 
@@ -36,7 +55,7 @@ End
 Encoding utf8x utf8x "Unicode (ucs-extended) (utf8x)" UTF-8 variable inputenc
 End
 
-# This encoding is used to typeset Armenian using the armTeX package
+# from http://www.ctan.org/pkg/armtex
 Encoding armscii8 armscii8 "Armenian (ArmSCII8)" ARMSCII-8 fixed inputenc
 End
 
@@ -52,14 +71,15 @@ End
 Encoding iso8859-4 latin4 "Baltic (ISO 8859-4)" ISO-8859-4 fixed inputenc
 End
 
+# from http://www.ctan.org/pkg/latex-cyrillic
 Encoding iso8859-5 iso88595 "Cyrillic (ISO 8859-5)" ISO-8859-5 fixed inputenc
 End
 
-# Not standard, see http://tug.ctan.org/tex-archive/language/arabic/arabi/arabi/texmf/latex/arabi/
+# from http://www.ctan.org/pkg/arabi
 Encoding iso8859-6 8859-6 "Arabic (ISO 8859-6)" ISO-8859-6 fixed inputenc
 End
 
-# Not standard, see http://ctan.org/tex-archive/language/greek/greek-inputenc
+# from http://www.ctan.org/pkg/greek-inputenc
 Encoding iso8859-7 iso-8859-7 "Greek (ISO 8859-7)" ISO-8859-7 fixed inputenc
 End
 
@@ -84,7 +104,7 @@ End
 Encoding cp437 cp437 "DOS (CP 437)" CP437 fixed inputenc
 End
 
-# cp437, but on position 225 is sz instead of beta
+# like cp437, but on position 225 is sz instead of beta
 Encoding cp437de cp437de "DOS-de (CP 437-de)" CP437 fixed inputenc
 End
 
@@ -94,10 +114,12 @@ End
 Encoding cp852 cp852 "Central European (CP 852)" CP852 fixed inputenc
 End
 
+# from http://www.ctan.org/pkg/latex-cyrillic
 Encoding cp855 cp855 "Cyrillic (CP 855)" CP855 fixed inputenc
 End
 
-# TODO: not supported by iconv (2.24 on Debian)
+# Gnu iconv only supports cp858, if configured with "--enable-extra-encodings"
+# (see https://www.gnu.org/software/libiconv/)
 Encoding cp858 cp858 "Western European (CP 858)" CP858 fixed inputenc
 End
 
@@ -107,12 +129,14 @@ End
 Encoding cp865 cp865 "Nordic languages (CP 865)" CP865 fixed inputenc
 End
 
+# from http://www.ctan.org/pkg/latex-cyrillic
 Encoding cp866 cp866 "Cyrillic (CP 866)" CP866 fixed inputenc
 End
 
 Encoding cp1250 cp1250 "Central European (CP 1250)" CP1250 fixed inputenc
 End
 
+# from http://www.ctan.org/pkg/latex-cyrillic
 Encoding cp1251 cp1251 "Cyrillic (CP 1251)" CP1251 fixed inputenc
 End
 
@@ -123,26 +147,25 @@ End
 Encoding cp1255 cp1255 "Hebrew (CP 1255)" CP1255 fixed inputenc
 End
 
-# Not standard, see http://tug.ctan.org/tex-archive/language/arabic/arabi/arabi/texmf/latex/arabi/
+# from http://www.ctan.org/pkg/arabi
 Encoding cp1256 cp1256 "Arabic (CP 1256)" CP1256 fixed inputenc
 End
 
 Encoding cp1257 cp1257 "Baltic (CP 1257)" CP1257 fixed inputenc
 End
 
+# from http://www.ctan.org/pkg/latex-cyrillic
 Encoding koi8-r koi8-r "Cyrillic (KOI8-R)" KOI8-R fixed inputenc
 End
 
+# from http://www.ctan.org/pkg/latex-cyrillic
 Encoding koi8-u koi8-u "Cyrillic (KOI8-U)" KOI8-U fixed inputenc
 End
 
+# from http://www.ctan.org/pkg/latex-cyrillic
 Encoding pt154 pt154 "Cyrillic (pt 154)" PT154 fixed inputenc
 End
 
-# TODO: not supported by iconv (2.24 on Debian)
-Encoding pt254 pt254 "Cyrillic (pt 254)" PT254 fixed inputenc
-End
-
 # encodings used by CJK.sty
 
 # The following encodings that are supported by the CJK package are not