From 2734d5800cfdc47784814bb117eff33f0b3c5aa1 Mon Sep 17 00:00:00 2001
From: Logan Hanks <logan@reddit.com>
Date: Thu, 16 Jun 2011 15:18:11 -0700
Subject: [PATCH] Add xhtml entity definitions via minimal DTD before parsing
 markdown output. Fixes issue #38.

---
 r2/r2/lib/contrib/dtds/README            |   2 +
 r2/r2/lib/contrib/dtds/xhtml-lat1.ent    | 196 +++++++++++++++++++
 r2/r2/lib/contrib/dtds/xhtml-special.ent |  80 ++++++++
 r2/r2/lib/contrib/dtds/xhtml-symbol.ent  | 237 +++++++++++++++++++++++
 r2/r2/lib/contrib/dtds/xhtml.dtd         |   9 +
 r2/r2/lib/filters.py                     |  16 +-
 6 files changed, 538 insertions(+), 2 deletions(-)
 create mode 100644 r2/r2/lib/contrib/dtds/README
 create mode 100644 r2/r2/lib/contrib/dtds/xhtml-lat1.ent
 create mode 100644 r2/r2/lib/contrib/dtds/xhtml-special.ent
 create mode 100644 r2/r2/lib/contrib/dtds/xhtml-symbol.ent
 create mode 100644 r2/r2/lib/contrib/dtds/xhtml.dtd

diff --git a/r2/r2/lib/contrib/dtds/README b/r2/r2/lib/contrib/dtds/README
new file mode 100644
index 000000000..232f12854
--- /dev/null
+++ b/r2/r2/lib/contrib/dtds/README
@@ -0,0 +1,2 @@
+This directory provides a minimal DTD defining XHTML entities, for parsing
+HTML generated by markdown.
diff --git a/r2/r2/lib/contrib/dtds/xhtml-lat1.ent b/r2/r2/lib/contrib/dtds/xhtml-lat1.ent
new file mode 100644
index 000000000..ffee223eb
--- /dev/null
+++ b/r2/r2/lib/contrib/dtds/xhtml-lat1.ent
@@ -0,0 +1,196 @@
+<!-- Portions (C) International Organization for Standardization 1986
+     Permission to copy in any form is granted for use with
+     conforming SGML systems and applications as defined in
+     ISO 8879, provided this notice is included in all copies.
+-->
+<!-- Character entity set. Typical invocation:
+    <!ENTITY % HTMLlat1 PUBLIC
+       "-//W3C//ENTITIES Latin 1 for XHTML//EN"
+       "http://www.w3.org/TR/xhtml1/DTD/xhtml-lat1.ent">
+    %HTMLlat1;
+-->
+
+<!ENTITY nbsp   "&#160;"> <!-- no-break space = non-breaking space,
+                                  U+00A0 ISOnum -->
+<!ENTITY iexcl  "&#161;"> <!-- inverted exclamation mark, U+00A1 ISOnum -->
+<!ENTITY cent   "&#162;"> <!-- cent sign, U+00A2 ISOnum -->
+<!ENTITY pound  "&#163;"> <!-- pound sign, U+00A3 ISOnum -->
+<!ENTITY curren "&#164;"> <!-- currency sign, U+00A4 ISOnum -->
+<!ENTITY yen    "&#165;"> <!-- yen sign = yuan sign, U+00A5 ISOnum -->
+<!ENTITY brvbar "&#166;"> <!-- broken bar = broken vertical bar,
+                                  U+00A6 ISOnum -->
+<!ENTITY sect   "&#167;"> <!-- section sign, U+00A7 ISOnum -->
+<!ENTITY uml    "&#168;"> <!-- diaeresis = spacing diaeresis,
+                                  U+00A8 ISOdia -->
+<!ENTITY copy   "&#169;"> <!-- copyright sign, U+00A9 ISOnum -->
+<!ENTITY ordf   "&#170;"> <!-- feminine ordinal indicator, U+00AA ISOnum -->
+<!ENTITY laquo  "&#171;"> <!-- left-pointing double angle quotation mark
+                                  = left pointing guillemet, U+00AB ISOnum -->
+<!ENTITY not    "&#172;"> <!-- not sign = angled dash,
+                                  U+00AC ISOnum -->
+<!ENTITY shy    "&#173;"> <!-- soft hyphen = discretionary hyphen,
+                                  U+00AD ISOnum -->
+<!ENTITY reg    "&#174;"> <!-- registered sign = registered trade mark sign,
+                                  U+00AE ISOnum -->
+<!ENTITY macr   "&#175;"> <!-- macron = spacing macron = overline
+                                  = APL overbar, U+00AF ISOdia -->
+<!ENTITY deg    "&#176;"> <!-- degree sign, U+00B0 ISOnum -->
+<!ENTITY plusmn "&#177;"> <!-- plus-minus sign = plus-or-minus sign,
+                                  U+00B1 ISOnum -->
+<!ENTITY sup2   "&#178;"> <!-- superscript two = superscript digit two
+                                  = squared, U+00B2 ISOnum -->
+<!ENTITY sup3   "&#179;"> <!-- superscript three = superscript digit three
+                                  = cubed, U+00B3 ISOnum -->
+<!ENTITY acute  "&#180;"> <!-- acute accent = spacing acute,
+                                  U+00B4 ISOdia -->
+<!ENTITY micro  "&#181;"> <!-- micro sign, U+00B5 ISOnum -->
+<!ENTITY para   "&#182;"> <!-- pilcrow sign = paragraph sign,
+                                  U+00B6 ISOnum -->
+<!ENTITY middot "&#183;"> <!-- middle dot = Georgian comma
+                                  = Greek middle dot, U+00B7 ISOnum -->
+<!ENTITY cedil  "&#184;"> <!-- cedilla = spacing cedilla, U+00B8 ISOdia -->
+<!ENTITY sup1   "&#185;"> <!-- superscript one = superscript digit one,
+                                  U+00B9 ISOnum -->
+<!ENTITY ordm   "&#186;"> <!-- masculine ordinal indicator,
+                                  U+00BA ISOnum -->
+<!ENTITY raquo  "&#187;"> <!-- right-pointing double angle quotation mark
+                                  = right pointing guillemet, U+00BB ISOnum -->
+<!ENTITY frac14 "&#188;"> <!-- vulgar fraction one quarter
+                                  = fraction one quarter, U+00BC ISOnum -->
+<!ENTITY frac12 "&#189;"> <!-- vulgar fraction one half
+                                  = fraction one half, U+00BD ISOnum -->
+<!ENTITY frac34 "&#190;"> <!-- vulgar fraction three quarters
+                                  = fraction three quarters, U+00BE ISOnum -->
+<!ENTITY iquest "&#191;"> <!-- inverted question mark
+                                  = turned question mark, U+00BF ISOnum -->
+<!ENTITY Agrave "&#192;"> <!-- latin capital letter A with grave
+                                  = latin capital letter A grave,
+                                  U+00C0 ISOlat1 -->
+<!ENTITY Aacute "&#193;"> <!-- latin capital letter A with acute,
+                                  U+00C1 ISOlat1 -->
+<!ENTITY Acirc  "&#194;"> <!-- latin capital letter A with circumflex,
+                                  U+00C2 ISOlat1 -->
+<!ENTITY Atilde "&#195;"> <!-- latin capital letter A with tilde,
+                                  U+00C3 ISOlat1 -->
+<!ENTITY Auml   "&#196;"> <!-- latin capital letter A with diaeresis,
+                                  U+00C4 ISOlat1 -->
+<!ENTITY Aring  "&#197;"> <!-- latin capital letter A with ring above
+                                  = latin capital letter A ring,
+                                  U+00C5 ISOlat1 -->
+<!ENTITY AElig  "&#198;"> <!-- latin capital letter AE
+                                  = latin capital ligature AE,
+                                  U+00C6 ISOlat1 -->
+<!ENTITY Ccedil "&#199;"> <!-- latin capital letter C with cedilla,
+                                  U+00C7 ISOlat1 -->
+<!ENTITY Egrave "&#200;"> <!-- latin capital letter E with grave,
+                                  U+00C8 ISOlat1 -->
+<!ENTITY Eacute "&#201;"> <!-- latin capital letter E with acute,
+                                  U+00C9 ISOlat1 -->
+<!ENTITY Ecirc  "&#202;"> <!-- latin capital letter E with circumflex,
+                                  U+00CA ISOlat1 -->
+<!ENTITY Euml   "&#203;"> <!-- latin capital letter E with diaeresis,
+                                  U+00CB ISOlat1 -->
+<!ENTITY Igrave "&#204;"> <!-- latin capital letter I with grave,
+                                  U+00CC ISOlat1 -->
+<!ENTITY Iacute "&#205;"> <!-- latin capital letter I with acute,
+                                  U+00CD ISOlat1 -->
+<!ENTITY Icirc  "&#206;"> <!-- latin capital letter I with circumflex,
+                                  U+00CE ISOlat1 -->
+<!ENTITY Iuml   "&#207;"> <!-- latin capital letter I with diaeresis,
+                                  U+00CF ISOlat1 -->
+<!ENTITY ETH    "&#208;"> <!-- latin capital letter ETH, U+00D0 ISOlat1 -->
+<!ENTITY Ntilde "&#209;"> <!-- latin capital letter N with tilde,
+                                  U+00D1 ISOlat1 -->
+<!ENTITY Ograve "&#210;"> <!-- latin capital letter O with grave,
+                                  U+00D2 ISOlat1 -->
+<!ENTITY Oacute "&#211;"> <!-- latin capital letter O with acute,
+                                  U+00D3 ISOlat1 -->
+<!ENTITY Ocirc  "&#212;"> <!-- latin capital letter O with circumflex,
+                                  U+00D4 ISOlat1 -->
+<!ENTITY Otilde "&#213;"> <!-- latin capital letter O with tilde,
+                                  U+00D5 ISOlat1 -->
+<!ENTITY Ouml   "&#214;"> <!-- latin capital letter O with diaeresis,
+                                  U+00D6 ISOlat1 -->
+<!ENTITY times  "&#215;"> <!-- multiplication sign, U+00D7 ISOnum -->
+<!ENTITY Oslash "&#216;"> <!-- latin capital letter O with stroke
+                                  = latin capital letter O slash,
+                                  U+00D8 ISOlat1 -->
+<!ENTITY Ugrave "&#217;"> <!-- latin capital letter U with grave,
+                                  U+00D9 ISOlat1 -->
+<!ENTITY Uacute "&#218;"> <!-- latin capital letter U with acute,
+                                  U+00DA ISOlat1 -->
+<!ENTITY Ucirc  "&#219;"> <!-- latin capital letter U with circumflex,
+                                  U+00DB ISOlat1 -->
+<!ENTITY Uuml   "&#220;"> <!-- latin capital letter U with diaeresis,
+                                  U+00DC ISOlat1 -->
+<!ENTITY Yacute "&#221;"> <!-- latin capital letter Y with acute,
+                                  U+00DD ISOlat1 -->
+<!ENTITY THORN  "&#222;"> <!-- latin capital letter THORN,
+                                  U+00DE ISOlat1 -->
+<!ENTITY szlig  "&#223;"> <!-- latin small letter sharp s = ess-zed,
+                                  U+00DF ISOlat1 -->
+<!ENTITY agrave "&#224;"> <!-- latin small letter a with grave
+                                  = latin small letter a grave,
+                                  U+00E0 ISOlat1 -->
+<!ENTITY aacute "&#225;"> <!-- latin small letter a with acute,
+                                  U+00E1 ISOlat1 -->
+<!ENTITY acirc  "&#226;"> <!-- latin small letter a with circumflex,
+                                  U+00E2 ISOlat1 -->
+<!ENTITY atilde "&#227;"> <!-- latin small letter a with tilde,
+                                  U+00E3 ISOlat1 -->
+<!ENTITY auml   "&#228;"> <!-- latin small letter a with diaeresis,
+                                  U+00E4 ISOlat1 -->
+<!ENTITY aring  "&#229;"> <!-- latin small letter a with ring above
+                                  = latin small letter a ring,
+                                  U+00E5 ISOlat1 -->
+<!ENTITY aelig  "&#230;"> <!-- latin small letter ae
+                                  = latin small ligature ae, U+00E6 ISOlat1 -->
+<!ENTITY ccedil "&#231;"> <!-- latin small letter c with cedilla,
+                                  U+00E7 ISOlat1 -->
+<!ENTITY egrave "&#232;"> <!-- latin small letter e with grave,
+                                  U+00E8 ISOlat1 -->
+<!ENTITY eacute "&#233;"> <!-- latin small letter e with acute,
+                                  U+00E9 ISOlat1 -->
+<!ENTITY ecirc  "&#234;"> <!-- latin small letter e with circumflex,
+                                  U+00EA ISOlat1 -->
+<!ENTITY euml   "&#235;"> <!-- latin small letter e with diaeresis,
+                                  U+00EB ISOlat1 -->
+<!ENTITY igrave "&#236;"> <!-- latin small letter i with grave,
+                                  U+00EC ISOlat1 -->
+<!ENTITY iacute "&#237;"> <!-- latin small letter i with acute,
+                                  U+00ED ISOlat1 -->
+<!ENTITY icirc  "&#238;"> <!-- latin small letter i with circumflex,
+                                  U+00EE ISOlat1 -->
+<!ENTITY iuml   "&#239;"> <!-- latin small letter i with diaeresis,
+                                  U+00EF ISOlat1 -->
+<!ENTITY eth    "&#240;"> <!-- latin small letter eth, U+00F0 ISOlat1 -->
+<!ENTITY ntilde "&#241;"> <!-- latin small letter n with tilde,
+                                  U+00F1 ISOlat1 -->
+<!ENTITY ograve "&#242;"> <!-- latin small letter o with grave,
+                                  U+00F2 ISOlat1 -->
+<!ENTITY oacute "&#243;"> <!-- latin small letter o with acute,
+                                  U+00F3 ISOlat1 -->
+<!ENTITY ocirc  "&#244;"> <!-- latin small letter o with circumflex,
+                                  U+00F4 ISOlat1 -->
+<!ENTITY otilde "&#245;"> <!-- latin small letter o with tilde,
+                                  U+00F5 ISOlat1 -->
+<!ENTITY ouml   "&#246;"> <!-- latin small letter o with diaeresis,
+                                  U+00F6 ISOlat1 -->
+<!ENTITY divide "&#247;"> <!-- division sign, U+00F7 ISOnum -->
+<!ENTITY oslash "&#248;"> <!-- latin small letter o with stroke,
+                                  = latin small letter o slash,
+                                  U+00F8 ISOlat1 -->
+<!ENTITY ugrave "&#249;"> <!-- latin small letter u with grave,
+                                  U+00F9 ISOlat1 -->
+<!ENTITY uacute "&#250;"> <!-- latin small letter u with acute,
+                                  U+00FA ISOlat1 -->
+<!ENTITY ucirc  "&#251;"> <!-- latin small letter u with circumflex,
+                                  U+00FB ISOlat1 -->
+<!ENTITY uuml   "&#252;"> <!-- latin small letter u with diaeresis,
+                                  U+00FC ISOlat1 -->
+<!ENTITY yacute "&#253;"> <!-- latin small letter y with acute,
+                                  U+00FD ISOlat1 -->
+<!ENTITY thorn  "&#254;"> <!-- latin small letter thorn,
+                                  U+00FE ISOlat1 -->
+<!ENTITY yuml   "&#255;"> <!-- latin small letter y with diaeresis,
+                                  U+00FF ISOlat1 -->
diff --git a/r2/r2/lib/contrib/dtds/xhtml-special.ent b/r2/r2/lib/contrib/dtds/xhtml-special.ent
new file mode 100644
index 000000000..ca358b2fe
--- /dev/null
+++ b/r2/r2/lib/contrib/dtds/xhtml-special.ent
@@ -0,0 +1,80 @@
+<!-- Special characters for XHTML -->
+
+<!-- Character entity set. Typical invocation:
+     <!ENTITY % HTMLspecial PUBLIC
+        "-//W3C//ENTITIES Special for XHTML//EN"
+        "http://www.w3.org/TR/xhtml1/DTD/xhtml-special.ent">
+     %HTMLspecial;
+-->
+
+<!-- Portions (C) International Organization for Standardization 1986:
+     Permission to copy in any form is granted for use with
+     conforming SGML systems and applications as defined in
+     ISO 8879, provided this notice is included in all copies.
+-->
+
+<!-- Relevant ISO entity set is given unless names are newly introduced.
+     New names (i.e., not in ISO 8879 list) do not clash with any
+     existing ISO 8879 entity names. ISO 10646 character numbers
+     are given for each character, in hex. values are decimal
+     conversions of the ISO 10646 values and refer to the document
+     character set. Names are Unicode names. 
+-->
+
+<!-- C0 Controls and Basic Latin -->
+<!ENTITY quot    "&#34;"> <!--  quotation mark, U+0022 ISOnum -->
+<!ENTITY amp     "&#38;#38;"> <!--  ampersand, U+0026 ISOnum -->
+<!ENTITY lt      "&#38;#60;"> <!--  less-than sign, U+003C ISOnum -->
+<!ENTITY gt      "&#62;"> <!--  greater-than sign, U+003E ISOnum -->
+<!ENTITY apos	 "&#39;"> <!--  apostrophe = APL quote, U+0027 ISOnum -->
+
+<!-- Latin Extended-A -->
+<!ENTITY OElig   "&#338;"> <!--  latin capital ligature OE,
+                                    U+0152 ISOlat2 -->
+<!ENTITY oelig   "&#339;"> <!--  latin small ligature oe, U+0153 ISOlat2 -->
+<!-- ligature is a misnomer, this is a separate character in some languages -->
+<!ENTITY Scaron  "&#352;"> <!--  latin capital letter S with caron,
+                                    U+0160 ISOlat2 -->
+<!ENTITY scaron  "&#353;"> <!--  latin small letter s with caron,
+                                    U+0161 ISOlat2 -->
+<!ENTITY Yuml    "&#376;"> <!--  latin capital letter Y with diaeresis,
+                                    U+0178 ISOlat2 -->
+
+<!-- Spacing Modifier Letters -->
+<!ENTITY circ    "&#710;"> <!--  modifier letter circumflex accent,
+                                    U+02C6 ISOpub -->
+<!ENTITY tilde   "&#732;"> <!--  small tilde, U+02DC ISOdia -->
+
+<!-- General Punctuation -->
+<!ENTITY ensp    "&#8194;"> <!-- en space, U+2002 ISOpub -->
+<!ENTITY emsp    "&#8195;"> <!-- em space, U+2003 ISOpub -->
+<!ENTITY thinsp  "&#8201;"> <!-- thin space, U+2009 ISOpub -->
+<!ENTITY zwnj    "&#8204;"> <!-- zero width non-joiner,
+                                    U+200C NEW RFC 2070 -->
+<!ENTITY zwj     "&#8205;"> <!-- zero width joiner, U+200D NEW RFC 2070 -->
+<!ENTITY lrm     "&#8206;"> <!-- left-to-right mark, U+200E NEW RFC 2070 -->
+<!ENTITY rlm     "&#8207;"> <!-- right-to-left mark, U+200F NEW RFC 2070 -->
+<!ENTITY ndash   "&#8211;"> <!-- en dash, U+2013 ISOpub -->
+<!ENTITY mdash   "&#8212;"> <!-- em dash, U+2014 ISOpub -->
+<!ENTITY lsquo   "&#8216;"> <!-- left single quotation mark,
+                                    U+2018 ISOnum -->
+<!ENTITY rsquo   "&#8217;"> <!-- right single quotation mark,
+                                    U+2019 ISOnum -->
+<!ENTITY sbquo   "&#8218;"> <!-- single low-9 quotation mark, U+201A NEW -->
+<!ENTITY ldquo   "&#8220;"> <!-- left double quotation mark,
+                                    U+201C ISOnum -->
+<!ENTITY rdquo   "&#8221;"> <!-- right double quotation mark,
+                                    U+201D ISOnum -->
+<!ENTITY bdquo   "&#8222;"> <!-- double low-9 quotation mark, U+201E NEW -->
+<!ENTITY dagger  "&#8224;"> <!-- dagger, U+2020 ISOpub -->
+<!ENTITY Dagger  "&#8225;"> <!-- double dagger, U+2021 ISOpub -->
+<!ENTITY permil  "&#8240;"> <!-- per mille sign, U+2030 ISOtech -->
+<!ENTITY lsaquo  "&#8249;"> <!-- single left-pointing angle quotation mark,
+                                    U+2039 ISO proposed -->
+<!-- lsaquo is proposed but not yet ISO standardized -->
+<!ENTITY rsaquo  "&#8250;"> <!-- single right-pointing angle quotation mark,
+                                    U+203A ISO proposed -->
+<!-- rsaquo is proposed but not yet ISO standardized -->
+
+<!-- Currency Symbols -->
+<!ENTITY euro   "&#8364;"> <!--  euro sign, U+20AC NEW -->
diff --git a/r2/r2/lib/contrib/dtds/xhtml-symbol.ent b/r2/r2/lib/contrib/dtds/xhtml-symbol.ent
new file mode 100644
index 000000000..63c2abfa6
--- /dev/null
+++ b/r2/r2/lib/contrib/dtds/xhtml-symbol.ent
@@ -0,0 +1,237 @@
+<!-- Mathematical, Greek and Symbolic characters for XHTML -->
+
+<!-- Character entity set. Typical invocation:
+     <!ENTITY % HTMLsymbol PUBLIC
+        "-//W3C//ENTITIES Symbols for XHTML//EN"
+        "http://www.w3.org/TR/xhtml1/DTD/xhtml-symbol.ent">
+     %HTMLsymbol;
+-->
+
+<!-- Portions (C) International Organization for Standardization 1986:
+     Permission to copy in any form is granted for use with
+     conforming SGML systems and applications as defined in
+     ISO 8879, provided this notice is included in all copies.
+-->
+
+<!-- Relevant ISO entity set is given unless names are newly introduced.
+     New names (i.e., not in ISO 8879 list) do not clash with any
+     existing ISO 8879 entity names. ISO 10646 character numbers
+     are given for each character, in hex. values are decimal
+     conversions of the ISO 10646 values and refer to the document
+     character set. Names are Unicode names. 
+-->
+
+<!-- Latin Extended-B -->
+<!ENTITY fnof     "&#402;"> <!-- latin small letter f with hook = function
+                                    = florin, U+0192 ISOtech -->
+
+<!-- Greek -->
+<!ENTITY Alpha    "&#913;"> <!-- greek capital letter alpha, U+0391 -->
+<!ENTITY Beta     "&#914;"> <!-- greek capital letter beta, U+0392 -->
+<!ENTITY Gamma    "&#915;"> <!-- greek capital letter gamma,
+                                    U+0393 ISOgrk3 -->
+<!ENTITY Delta    "&#916;"> <!-- greek capital letter delta,
+                                    U+0394 ISOgrk3 -->
+<!ENTITY Epsilon  "&#917;"> <!-- greek capital letter epsilon, U+0395 -->
+<!ENTITY Zeta     "&#918;"> <!-- greek capital letter zeta, U+0396 -->
+<!ENTITY Eta      "&#919;"> <!-- greek capital letter eta, U+0397 -->
+<!ENTITY Theta    "&#920;"> <!-- greek capital letter theta,
+                                    U+0398 ISOgrk3 -->
+<!ENTITY Iota     "&#921;"> <!-- greek capital letter iota, U+0399 -->
+<!ENTITY Kappa    "&#922;"> <!-- greek capital letter kappa, U+039A -->
+<!ENTITY Lambda   "&#923;"> <!-- greek capital letter lamda,
+                                    U+039B ISOgrk3 -->
+<!ENTITY Mu       "&#924;"> <!-- greek capital letter mu, U+039C -->
+<!ENTITY Nu       "&#925;"> <!-- greek capital letter nu, U+039D -->
+<!ENTITY Xi       "&#926;"> <!-- greek capital letter xi, U+039E ISOgrk3 -->
+<!ENTITY Omicron  "&#927;"> <!-- greek capital letter omicron, U+039F -->
+<!ENTITY Pi       "&#928;"> <!-- greek capital letter pi, U+03A0 ISOgrk3 -->
+<!ENTITY Rho      "&#929;"> <!-- greek capital letter rho, U+03A1 -->
+<!-- there is no Sigmaf, and no U+03A2 character either -->
+<!ENTITY Sigma    "&#931;"> <!-- greek capital letter sigma,
+                                    U+03A3 ISOgrk3 -->
+<!ENTITY Tau      "&#932;"> <!-- greek capital letter tau, U+03A4 -->
+<!ENTITY Upsilon  "&#933;"> <!-- greek capital letter upsilon,
+                                    U+03A5 ISOgrk3 -->
+<!ENTITY Phi      "&#934;"> <!-- greek capital letter phi,
+                                    U+03A6 ISOgrk3 -->
+<!ENTITY Chi      "&#935;"> <!-- greek capital letter chi, U+03A7 -->
+<!ENTITY Psi      "&#936;"> <!-- greek capital letter psi,
+                                    U+03A8 ISOgrk3 -->
+<!ENTITY Omega    "&#937;"> <!-- greek capital letter omega,
+                                    U+03A9 ISOgrk3 -->
+
+<!ENTITY alpha    "&#945;"> <!-- greek small letter alpha,
+                                    U+03B1 ISOgrk3 -->
+<!ENTITY beta     "&#946;"> <!-- greek small letter beta, U+03B2 ISOgrk3 -->
+<!ENTITY gamma    "&#947;"> <!-- greek small letter gamma,
+                                    U+03B3 ISOgrk3 -->
+<!ENTITY delta    "&#948;"> <!-- greek small letter delta,
+                                    U+03B4 ISOgrk3 -->
+<!ENTITY epsilon  "&#949;"> <!-- greek small letter epsilon,
+                                    U+03B5 ISOgrk3 -->
+<!ENTITY zeta     "&#950;"> <!-- greek small letter zeta, U+03B6 ISOgrk3 -->
+<!ENTITY eta      "&#951;"> <!-- greek small letter eta, U+03B7 ISOgrk3 -->
+<!ENTITY theta    "&#952;"> <!-- greek small letter theta,
+                                    U+03B8 ISOgrk3 -->
+<!ENTITY iota     "&#953;"> <!-- greek small letter iota, U+03B9 ISOgrk3 -->
+<!ENTITY kappa    "&#954;"> <!-- greek small letter kappa,
+                                    U+03BA ISOgrk3 -->
+<!ENTITY lambda   "&#955;"> <!-- greek small letter lamda,
+                                    U+03BB ISOgrk3 -->
+<!ENTITY mu       "&#956;"> <!-- greek small letter mu, U+03BC ISOgrk3 -->
+<!ENTITY nu       "&#957;"> <!-- greek small letter nu, U+03BD ISOgrk3 -->
+<!ENTITY xi       "&#958;"> <!-- greek small letter xi, U+03BE ISOgrk3 -->
+<!ENTITY omicron  "&#959;"> <!-- greek small letter omicron, U+03BF NEW -->
+<!ENTITY pi       "&#960;"> <!-- greek small letter pi, U+03C0 ISOgrk3 -->
+<!ENTITY rho      "&#961;"> <!-- greek small letter rho, U+03C1 ISOgrk3 -->
+<!ENTITY sigmaf   "&#962;"> <!-- greek small letter final sigma,
+                                    U+03C2 ISOgrk3 -->
+<!ENTITY sigma    "&#963;"> <!-- greek small letter sigma,
+                                    U+03C3 ISOgrk3 -->
+<!ENTITY tau      "&#964;"> <!-- greek small letter tau, U+03C4 ISOgrk3 -->
+<!ENTITY upsilon  "&#965;"> <!-- greek small letter upsilon,
+                                    U+03C5 ISOgrk3 -->
+<!ENTITY phi      "&#966;"> <!-- greek small letter phi, U+03C6 ISOgrk3 -->
+<!ENTITY chi      "&#967;"> <!-- greek small letter chi, U+03C7 ISOgrk3 -->
+<!ENTITY psi      "&#968;"> <!-- greek small letter psi, U+03C8 ISOgrk3 -->
+<!ENTITY omega    "&#969;"> <!-- greek small letter omega,
+                                    U+03C9 ISOgrk3 -->
+<!ENTITY thetasym "&#977;"> <!-- greek theta symbol,
+                                    U+03D1 NEW -->
+<!ENTITY upsih    "&#978;"> <!-- greek upsilon with hook symbol,
+                                    U+03D2 NEW -->
+<!ENTITY piv      "&#982;"> <!-- greek pi symbol, U+03D6 ISOgrk3 -->
+
+<!-- General Punctuation -->
+<!ENTITY bull     "&#8226;"> <!-- bullet = black small circle,
+                                     U+2022 ISOpub  -->
+<!-- bullet is NOT the same as bullet operator, U+2219 -->
+<!ENTITY hellip   "&#8230;"> <!-- horizontal ellipsis = three dot leader,
+                                     U+2026 ISOpub  -->
+<!ENTITY prime    "&#8242;"> <!-- prime = minutes = feet, U+2032 ISOtech -->
+<!ENTITY Prime    "&#8243;"> <!-- double prime = seconds = inches,
+                                     U+2033 ISOtech -->
+<!ENTITY oline    "&#8254;"> <!-- overline = spacing overscore,
+                                     U+203E NEW -->
+<!ENTITY frasl    "&#8260;"> <!-- fraction slash, U+2044 NEW -->
+
+<!-- Letterlike Symbols -->
+<!ENTITY weierp   "&#8472;"> <!-- script capital P = power set
+                                     = Weierstrass p, U+2118 ISOamso -->
+<!ENTITY image    "&#8465;"> <!-- black-letter capital I = imaginary part,
+                                     U+2111 ISOamso -->
+<!ENTITY real     "&#8476;"> <!-- black-letter capital R = real part symbol,
+                                     U+211C ISOamso -->
+<!ENTITY trade    "&#8482;"> <!-- trade mark sign, U+2122 ISOnum -->
+<!ENTITY alefsym  "&#8501;"> <!-- alef symbol = first transfinite cardinal,
+                                     U+2135 NEW -->
+<!-- alef symbol is NOT the same as hebrew letter alef,
+     U+05D0 although the same glyph could be used to depict both characters -->
+
+<!-- Arrows -->
+<!ENTITY larr     "&#8592;"> <!-- leftwards arrow, U+2190 ISOnum -->
+<!ENTITY uarr     "&#8593;"> <!-- upwards arrow, U+2191 ISOnum-->
+<!ENTITY rarr     "&#8594;"> <!-- rightwards arrow, U+2192 ISOnum -->
+<!ENTITY darr     "&#8595;"> <!-- downwards arrow, U+2193 ISOnum -->
+<!ENTITY harr     "&#8596;"> <!-- left right arrow, U+2194 ISOamsa -->
+<!ENTITY crarr    "&#8629;"> <!-- downwards arrow with corner leftwards
+                                     = carriage return, U+21B5 NEW -->
+<!ENTITY lArr     "&#8656;"> <!-- leftwards double arrow, U+21D0 ISOtech -->
+<!-- Unicode does not say that lArr is the same as the 'is implied by' arrow
+    but also does not have any other character for that function. So lArr can
+    be used for 'is implied by' as ISOtech suggests -->
+<!ENTITY uArr     "&#8657;"> <!-- upwards double arrow, U+21D1 ISOamsa -->
+<!ENTITY rArr     "&#8658;"> <!-- rightwards double arrow,
+                                     U+21D2 ISOtech -->
+<!-- Unicode does not say this is the 'implies' character but does not have 
+     another character with this function so rArr can be used for 'implies'
+     as ISOtech suggests -->
+<!ENTITY dArr     "&#8659;"> <!-- downwards double arrow, U+21D3 ISOamsa -->
+<!ENTITY hArr     "&#8660;"> <!-- left right double arrow,
+                                     U+21D4 ISOamsa -->
+
+<!-- Mathematical Operators -->
+<!ENTITY forall   "&#8704;"> <!-- for all, U+2200 ISOtech -->
+<!ENTITY part     "&#8706;"> <!-- partial differential, U+2202 ISOtech  -->
+<!ENTITY exist    "&#8707;"> <!-- there exists, U+2203 ISOtech -->
+<!ENTITY empty    "&#8709;"> <!-- empty set = null set, U+2205 ISOamso -->
+<!ENTITY nabla    "&#8711;"> <!-- nabla = backward difference,
+                                     U+2207 ISOtech -->
+<!ENTITY isin     "&#8712;"> <!-- element of, U+2208 ISOtech -->
+<!ENTITY notin    "&#8713;"> <!-- not an element of, U+2209 ISOtech -->
+<!ENTITY ni       "&#8715;"> <!-- contains as member, U+220B ISOtech -->
+<!ENTITY prod     "&#8719;"> <!-- n-ary product = product sign,
+                                     U+220F ISOamsb -->
+<!-- prod is NOT the same character as U+03A0 'greek capital letter pi' though
+     the same glyph might be used for both -->
+<!ENTITY sum      "&#8721;"> <!-- n-ary summation, U+2211 ISOamsb -->
+<!-- sum is NOT the same character as U+03A3 'greek capital letter sigma'
+     though the same glyph might be used for both -->
+<!ENTITY minus    "&#8722;"> <!-- minus sign, U+2212 ISOtech -->
+<!ENTITY lowast   "&#8727;"> <!-- asterisk operator, U+2217 ISOtech -->
+<!ENTITY radic    "&#8730;"> <!-- square root = radical sign,
+                                     U+221A ISOtech -->
+<!ENTITY prop     "&#8733;"> <!-- proportional to, U+221D ISOtech -->
+<!ENTITY infin    "&#8734;"> <!-- infinity, U+221E ISOtech -->
+<!ENTITY ang      "&#8736;"> <!-- angle, U+2220 ISOamso -->
+<!ENTITY and      "&#8743;"> <!-- logical and = wedge, U+2227 ISOtech -->
+<!ENTITY or       "&#8744;"> <!-- logical or = vee, U+2228 ISOtech -->
+<!ENTITY cap      "&#8745;"> <!-- intersection = cap, U+2229 ISOtech -->
+<!ENTITY cup      "&#8746;"> <!-- union = cup, U+222A ISOtech -->
+<!ENTITY int      "&#8747;"> <!-- integral, U+222B ISOtech -->
+<!ENTITY there4   "&#8756;"> <!-- therefore, U+2234 ISOtech -->
+<!ENTITY sim      "&#8764;"> <!-- tilde operator = varies with = similar to,
+                                     U+223C ISOtech -->
+<!-- tilde operator is NOT the same character as the tilde, U+007E,
+     although the same glyph might be used to represent both  -->
+<!ENTITY cong     "&#8773;"> <!-- approximately equal to, U+2245 ISOtech -->
+<!ENTITY asymp    "&#8776;"> <!-- almost equal to = asymptotic to,
+                                     U+2248 ISOamsr -->
+<!ENTITY ne       "&#8800;"> <!-- not equal to, U+2260 ISOtech -->
+<!ENTITY equiv    "&#8801;"> <!-- identical to, U+2261 ISOtech -->
+<!ENTITY le       "&#8804;"> <!-- less-than or equal to, U+2264 ISOtech -->
+<!ENTITY ge       "&#8805;"> <!-- greater-than or equal to,
+                                     U+2265 ISOtech -->
+<!ENTITY sub      "&#8834;"> <!-- subset of, U+2282 ISOtech -->
+<!ENTITY sup      "&#8835;"> <!-- superset of, U+2283 ISOtech -->
+<!ENTITY nsub     "&#8836;"> <!-- not a subset of, U+2284 ISOamsn -->
+<!ENTITY sube     "&#8838;"> <!-- subset of or equal to, U+2286 ISOtech -->
+<!ENTITY supe     "&#8839;"> <!-- superset of or equal to,
+                                     U+2287 ISOtech -->
+<!ENTITY oplus    "&#8853;"> <!-- circled plus = direct sum,
+                                     U+2295 ISOamsb -->
+<!ENTITY otimes   "&#8855;"> <!-- circled times = vector product,
+                                     U+2297 ISOamsb -->
+<!ENTITY perp     "&#8869;"> <!-- up tack = orthogonal to = perpendicular,
+                                     U+22A5 ISOtech -->
+<!ENTITY sdot     "&#8901;"> <!-- dot operator, U+22C5 ISOamsb -->
+<!-- dot operator is NOT the same character as U+00B7 middle dot -->
+
+<!-- Miscellaneous Technical -->
+<!ENTITY lceil    "&#8968;"> <!-- left ceiling = APL upstile,
+                                     U+2308 ISOamsc  -->
+<!ENTITY rceil    "&#8969;"> <!-- right ceiling, U+2309 ISOamsc  -->
+<!ENTITY lfloor   "&#8970;"> <!-- left floor = APL downstile,
+                                     U+230A ISOamsc  -->
+<!ENTITY rfloor   "&#8971;"> <!-- right floor, U+230B ISOamsc  -->
+<!ENTITY lang     "&#9001;"> <!-- left-pointing angle bracket = bra,
+                                     U+2329 ISOtech -->
+<!-- lang is NOT the same character as U+003C 'less than sign' 
+     or U+2039 'single left-pointing angle quotation mark' -->
+<!ENTITY rang     "&#9002;"> <!-- right-pointing angle bracket = ket,
+                                     U+232A ISOtech -->
+<!-- rang is NOT the same character as U+003E 'greater than sign' 
+     or U+203A 'single right-pointing angle quotation mark' -->
+
+<!-- Geometric Shapes -->
+<!ENTITY loz      "&#9674;"> <!-- lozenge, U+25CA ISOpub -->
+
+<!-- Miscellaneous Symbols -->
+<!ENTITY spades   "&#9824;"> <!-- black spade suit, U+2660 ISOpub -->
+<!-- black here seems to mean filled as opposed to hollow -->
+<!ENTITY clubs    "&#9827;"> <!-- black club suit = shamrock,
+                                     U+2663 ISOpub -->
+<!ENTITY hearts   "&#9829;"> <!-- black heart suit = valentine,
+                                     U+2665 ISOpub -->
+<!ENTITY diams    "&#9830;"> <!-- black diamond suit, U+2666 ISOpub -->
diff --git a/r2/r2/lib/contrib/dtds/xhtml.dtd b/r2/r2/lib/contrib/dtds/xhtml.dtd
new file mode 100644
index 000000000..b935f3214
--- /dev/null
+++ b/r2/r2/lib/contrib/dtds/xhtml.dtd
@@ -0,0 +1,9 @@
+<!ENTITY % HTMLlat1 SYSTEM "xhtml-lat1.ent">
+%HTMLlat1;
+
+<!ENTITY % HTMLspecial SYSTEM "xhtml-special.ent">
+%HTMLspecial;
+
+<!ENTITY % HTMLsymbol SYSTEM "xhtml-symbol.ent">
+%HTMLsymbol;
+
diff --git a/r2/r2/lib/filters.py b/r2/r2/lib/filters.py
index a54b92771..73920846b 100644
--- a/r2/r2/lib/filters.py
+++ b/r2/r2/lib/filters.py
@@ -20,6 +20,7 @@
 # CondeNet, Inc. All Rights Reserved.
 ################################################################################
 import cgi
+import os
 import urllib
 import re
 from cStringIO import StringIO
@@ -166,14 +167,25 @@ markdown_boring_tags =  ('p', 'em', 'strong', 'br', 'ol', 'ul', 'hr', 'li',
 for bt in markdown_boring_tags:
     markdown_ok_tags[bt] = ()
 
+markdown_xhtml_dtd_path = os.path.join(
+    os.path.dirname(os.path.abspath(__file__)),
+    'contrib/dtds/xhtml.dtd')
+
+markdown_dtd = '<!DOCTYPE div- SYSTEM "file://%s">' % markdown_xhtml_dtd_path
+
 def markdown_souptest(text, nofollow=False, target=None, lang=None):
     if not text:
         return text
 
     smd = safemarkdown(text, nofollow, target, lang)
 
-    s = StringIO(smd)
-    tree = lxml.etree.parse(s)
+    # Prepend a DTD reference so we can load up definitions of all the standard
+    # XHTML entities (&nbsp;, etc.).
+    smd_with_dtd = markdown_dtd + smd
+
+    s = StringIO(smd_with_dtd)
+    parser = lxml.etree.XMLParser(load_dtd=True)
+    tree = lxml.etree.parse(s, parser)
     handler = SouptestSaxHandler(markdown_ok_tags)
     saxify(tree, handler)