diff --git a/src/attrs.c b/src/attrs.c
index 983caee..f678245 100644
--- a/src/attrs.c
+++ b/src/attrs.c
@@ -479,11 +479,12 @@ uint TY_(NodeAttributeVersions)( Node* node, TidyAttrId id )
     return VERS_UNKNOWN;
 }
 
-/* returns true if the element is a W3C defined element */
-/* but the element/attribute combination is not. We're  */
-/* only defining as "proprietary" items that are not in */
-/* the element's AttrVersion structure.                 */
-static Bool AttributeIsProprietary(Node* node, AttVal* attval)
+/* returns true if the element is a W3C defined element
+ * but the element/attribute combination is not. We're
+ * only defining as "proprietary" items that are not in
+ * the element's AttrVersion structure.
+ */
+Bool TY_(AttributeIsProprietary)(Node* node, AttVal* attval)
 {
     if (!node || !attval)
         return no;
@@ -500,6 +501,34 @@ static Bool AttributeIsProprietary(Node* node, AttVal* attval)
     return yes;
 }
 
+/* returns true if the element is a W3C defined element
+ * but the element/attribute combination is not. We're
+ * considering it a mismatch if the document version
+ * does not allow the attribute as called out in its
+ * AttrVersion structure.
+ */
+Bool TY_(AttributeIsMismatched)(Node* node, AttVal* attval, TidyDocImpl* doc)
+{
+    uint doctype;
+    
+    if (!node || !attval)
+        return no;
+    
+    if (!node->tag)
+        return no;
+    
+    if (!(node->tag->versions & VERS_ALL))
+        return no;
+
+    doctype = doc->lexer->versionEmitted == 0 ? doc->lexer->doctype : doc->lexer->versionEmitted;
+
+    if (AttributeVersions(node, attval) & doctype)
+        return no;
+    
+    return yes;
+}
+
+
 /* used by CheckColor() */
 struct _colors
 {
@@ -1358,14 +1387,6 @@ const Attribute* TY_(CheckAttribute)( TidyDocImpl* doc, Node *node, AttVal *attv
             attribute->attrchk( doc, node, attval );
     }
 
-    if (AttributeIsProprietary(node, attval))
-    {
-        TY_(ReportAttrError)(doc, node, attval, PROPRIETARY_ATTRIBUTE);
-
-        if (cfgBool(doc, TidyDropPropAttrs))
-            TY_(RemoveAttribute)( doc, node, attval );
-    }
-
     return attribute;
 }
 
diff --git a/src/attrs.h b/src/attrs.h
index 2a70faf..e5b0fa9 100644
--- a/src/attrs.h
+++ b/src/attrs.h
@@ -147,6 +147,10 @@ AttVal* TY_(AttrGetById)( Node* node, TidyAttrId id );
 
 uint TY_(NodeAttributeVersions)( Node* node, TidyAttrId id );
 
+Bool TY_(AttributeIsProprietary)(Node* node, AttVal* attval);
+Bool TY_(AttributeIsMismatched)(Node* node, AttVal* attval, TidyDocImpl* doc);
+
+
 /* 0 == TidyAttr_UNKNOWN  */
 #define AttrId(av) ((av) && (av)->dict ? (av)->dict->id : TidyAttr_UNKNOWN)
 #define AttrIsId(av, atid) ((av) && (av)->dict && ((av)->dict->id == atid))
diff --git a/src/language.c b/src/language.c
index 6d60389..1959409 100644
--- a/src/language.c
+++ b/src/language.c
@@ -262,6 +262,8 @@ static const tidyErrorFilterKeyItem tidyErrorFilterKeysStruct[] = {
     { "CANT_BE_NESTED",                                CANT_BE_NESTED                                },
     { "OBSOLETE_ELEMENT",                              OBSOLETE_ELEMENT                              },
     { "PROPRIETARY_ELEMENT",                           PROPRIETARY_ELEMENT                           },
+    { "ELEMENT_VERS_MISMATCH_ERROR",                   ELEMENT_VERS_MISMATCH_ERROR                   },
+    { "ELEMENT_VERS_MISMATCH_WARN",                    ELEMENT_VERS_MISMATCH_WARN                    },
     { "UNKNOWN_ELEMENT",                               UNKNOWN_ELEMENT                               },
     { "TRIM_EMPTY_ELEMENT",                            TRIM_EMPTY_ELEMENT                            },
     { "COERCE_TO_ENDTAG",                              COERCE_TO_ENDTAG                              },
@@ -298,6 +300,8 @@ static const tidyErrorFilterKeyItem tidyErrorFilterKeysStruct[] = {
     { "BAD_ATTRIBUTE_VALUE",                           BAD_ATTRIBUTE_VALUE                           },
     { "UNEXPECTED_GT",                                 UNEXPECTED_GT                                 },
     { "PROPRIETARY_ATTRIBUTE",                         PROPRIETARY_ATTRIBUTE                         },
+    { "MISMATCHED_ATTRIBUTE_ERROR",                    MISMATCHED_ATTRIBUTE_ERROR                    },
+    { "MISMATCHED_ATTRIBUTE_WARN",                     MISMATCHED_ATTRIBUTE_WARN                     },
     { "PROPRIETARY_ATTR_VALUE",                        PROPRIETARY_ATTR_VALUE                        },
     { "REPEATED_ATTRIBUTE",                            REPEATED_ATTRIBUTE                            },
     { "MISSING_IMAGEMAP",                              MISSING_IMAGEMAP                              },
@@ -322,8 +326,6 @@ static const tidyErrorFilterKeyItem tidyErrorFilterKeysStruct[] = {
     { "MISSING_ATTRIBUTE",                             MISSING_ATTRIBUTE                             },
     { "WHITE_IN_URI",                                  WHITE_IN_URI                                  },
     { "REMOVED_HTML5",                                 REMOVED_HTML5                                 },
-    { "BAD_BODY_HTML5",                                BAD_BODY_HTML5                                },
-    { "BAD_ALIGN_HTML5",                               BAD_ALIGN_HTML5                               },
     { "BAD_SUMMARY_HTML5",                             BAD_SUMMARY_HTML5                             },
     { "PREVIOUS_LOCATION",                             PREVIOUS_LOCATION                             },
     { "VENDOR_SPECIFIC_CHARS",                         VENDOR_SPECIFIC_CHARS                         },
diff --git a/src/language_en.h b/src/language_en.h
index fbfb1a8..a06d58c 100644
--- a/src/language_en.h
+++ b/src/language_en.h
@@ -350,6 +350,8 @@ static languageDefinition language_en = { whichPluralForm_en, {
     { MISSING_ATTR_VALUE,           0,   "%s attribute \"%s\" lacks value"                                         }, /* Warning in CheckUrl, Error otherwise */
     { UNKNOWN_ATTRIBUTE,            0,   "%s unknown attribute \"%s\""                                             }, /* Error */
     { PROPRIETARY_ATTRIBUTE,        0,   "%s proprietary attribute \"%s\""                                         }, /* Error */
+    { MISMATCHED_ATTRIBUTE_ERROR,   0,   "%s attribute \"%s\" not allowed for %s"                                  }, /* Error */
+    { MISMATCHED_ATTRIBUTE_WARN,    0,   "%s attribute \"%s\" not allowed for %s"                                  }, /* Warning */
     { JOINING_ATTRIBUTE,            0,   "%s joining values of repeated attribute \"%s\""                          }, /* Error */
     { XML_ATTRIBUTE_VALUE,          0,   "%s has XML attribute \"%s\""                                             }, /* Error (but deprecated) */
     
@@ -392,8 +394,6 @@ static languageDefinition language_en = { whichPluralForm_en, {
     { OBSOLETE_ELEMENT,             0,   "replacing obsolete element %s with %s"                                   }, /* Warning */
     { COERCE_TO_ENDTAG_WARN,        0,   "<%s> is probably intended as </%s>"                                      }, /* Warning */
     { REMOVED_HTML5,                0,   "%s element removed from HTML5"                                           }, /* Warning */
-    { BAD_BODY_HTML5,               0,   "Found attribute on body that is obsolete in HTML5. Use CSS"              }, /* Warning */
-    { BAD_ALIGN_HTML5,              0,   "The align attribute on the %s element is obsolete. Use CSS"              }, /* Warning */
     { BAD_SUMMARY_HTML5,            0,   "The summary attribute on the %s element is obsolete in HTML5"            }, /* Warning */
     
     /* ReportNotice */
@@ -415,6 +415,8 @@ static languageDefinition language_en = { whichPluralForm_en, {
     { INSERTING_TAG,                0,   "inserting implicit <%s>"                                                 }, /* Error */
     { CANT_BE_NESTED,               0,   "%s can't be nested"                                                      }, /* Error */
     { PROPRIETARY_ELEMENT,          0,   "%s is not approved by W3C"                                               }, /* Error */
+    { ELEMENT_VERS_MISMATCH_ERROR,  0,   "%s element not available in %s"                                          }, /* Error */
+    { ELEMENT_VERS_MISMATCH_WARN,   0,   "%s element not available in %s"                                          }, /* Warning */
     { ILLEGAL_NESTING,              0,   "%s shouldn't be nested"                                                  }, /* Error */
     { NOFRAMES_CONTENT,             0,   "%s not inside 'noframes' element"                                        }, /* Error */
     { UNEXPECTED_END_OF_FILE,       0,   "unexpected end of file %s"                                               }, /* Error */
@@ -745,7 +747,9 @@ static languageDefinition language_en = { whichPluralForm_en, {
         - The strings "Tidy" and "HTML Tidy" are the program name and must not be translated. */
       TidyDropPropAttrs,            0,
         "This option specifies if Tidy should strip out proprietary attributes, "
-        "such as Microsoft data binding attributes. "
+        "such as Microsoft data binding attributes. Additionally attributes "
+        "that aren't permitted in the output version of HTML will be dropped "
+        "if used with <code>strict-tags-attributes</code>. "
     },
     {/* Please use _only_ <code></code>, <em></em>, <strong></strong>, and <br/>.
         It's very important that <br/> be self-closing in this manner! 
@@ -1574,6 +1578,21 @@ static languageDefinition language_en = { whichPluralForm_en, {
         "This option specifies that Tidy should skip nested tags when parsing "
         "script and style data. "
     },
+    {/* Please use _only_ <code></code>, <em></em>, <strong></strong>, and <br/>.
+        It's very important that <br/> be self-closing in this manner! 
+        - The strings "Tidy" and "HTML Tidy" are the program name and must not be translated. */
+      TidyStrictTagsAttr,           0,
+        "This options ensures that tags and attributes are applicable for the "
+        "version of HTML that Tidy outputs. When set to <code>yes</code> (the "
+        "default) and the output document type is a strict doctype, then Tidy "
+        "will report errors. If the output document type is a loose or "
+        "transitional doctype, then Tidy will report warnings. "
+        "<br/>"
+        "Additionally if <code>drop-proprietary-attributes</code> is enabled, "
+        "then not applicable attributes will be dropped, too. "
+        "<br/>"
+        "When set to <code>no</code>, these checks are not performed. "
+    },
     
     /********************************************************
      ** Console Application
diff --git a/src/lexer.c b/src/lexer.c
index 24b2343..00193a8 100644
--- a/src/lexer.c
+++ b/src/lexer.c
@@ -2709,26 +2709,8 @@ static Node* GetTokenFromStream( TidyDocImpl* doc, GetTokenMode mode )
                 {
                     Node* curr = lexer->token;
                     TY_(ConstrainVersion)( doc, curr->tag->versions );
-                    
-                    if ( curr->tag->versions & VERS_PROPRIETARY )
-                    {
-                        if ( !cfgBool(doc, TidyMakeClean) ||
-                             ( !nodeIsNOBR(curr) && !nodeIsWBR(curr) ) )
-                        {
-                            TY_(ReportError)(doc, NULL, curr, PROPRIETARY_ELEMENT );
-
-                            if ( nodeIsLAYER(curr) )
-                                doc->badLayout |= USING_LAYER;
-                            else if ( nodeIsSPACER(curr) )
-                                doc->badLayout |= USING_SPACER;
-                            else if ( nodeIsNOBR(curr) )
-                                doc->badLayout |= USING_NOBR;
-                        }
-                    }
-
-                    TY_(RepairDuplicateAttributes)( doc, curr, no );
-                } else 
                     TY_(RepairDuplicateAttributes)( doc, lexer->token, yes );
+                    
 #ifdef TIDY_STORE_ORIGINAL_TEXT
                 StoreOriginalTextInToken(doc, lexer->token, 0);
 #endif
diff --git a/src/message.c b/src/message.c
index be82246..2328515 100755
--- a/src/message.c
+++ b/src/message.c
@@ -525,6 +525,8 @@ void TY_(ReportAttrError)(TidyDocImpl* doc, Node *node, AttVal *av, uint code)
     char const *name = "NULL", *value = "NULL";
     char tagdesc[64];
     ctmbstr fmt = tidyLocalizedString(code);
+    uint version;
+    ctmbstr extra_string;
 
     assert( fmt != NULL );
 
@@ -549,6 +551,22 @@ void TY_(ReportAttrError)(TidyDocImpl* doc, Node *node, AttVal *av, uint code)
         messageNode(doc, TidyWarning, code, node, fmt, tagdesc, name);
         break;
 
+    case MISMATCHED_ATTRIBUTE_WARN:
+        version = doc->lexer->versionEmitted == 0 ? doc->lexer->doctype : doc->lexer->versionEmitted;
+        extra_string = TY_(HTMLVersionNameFromCode)(version, 0);
+        if (!extra_string)
+            extra_string = tidyLocalizedString(STRING_HTML_PROPRIETARY);
+        messageNode(doc, TidyWarning, code, node, fmt, tagdesc, name, extra_string);
+        break;
+
+    case MISMATCHED_ATTRIBUTE_ERROR:
+        version = doc->lexer->versionEmitted == 0 ? doc->lexer->doctype : doc->lexer->versionEmitted;
+        extra_string = TY_(HTMLVersionNameFromCode)(version, 0);
+        if (!extra_string)
+            extra_string = tidyLocalizedString(STRING_HTML_PROPRIETARY);
+        messageNode(doc, TidyError, code, node, fmt, tagdesc, name, extra_string);
+        break;
+
     case BAD_ATTRIBUTE_VALUE:
     case BAD_ATTRIBUTE_VALUE_REPLACED:
     case INVALID_ATTRIBUTE:
@@ -665,8 +683,6 @@ void TY_(ReportWarning)(TidyDocImpl* doc, Node *element, Node *node, uint code)
 
     case NESTED_EMPHASIS:
     case REMOVED_HTML5:
-    case BAD_BODY_HTML5:
-    case BAD_ALIGN_HTML5:
     case BAD_SUMMARY_HTML5:
         messageNode(doc, TidyWarning, code, rpt, fmt, nodedesc);
         break;
@@ -707,6 +723,8 @@ void TY_(ReportError)(TidyDocImpl* doc, Node *element, Node *node, uint code)
     char elemdesc[ 256 ] = {0};
     Node* rpt = ( element ? element : node );
     ctmbstr fmt = tidyLocalizedString(code);
+    uint versionEmitted, declared, version;
+    ctmbstr extra_string = NULL;
 
     assert( fmt != NULL );
 
@@ -729,6 +747,26 @@ void TY_(ReportError)(TidyDocImpl* doc, Node *element, Node *node, uint code)
         messageNode(doc, TidyWarning, code, node, fmt, nodedesc);
         break;
 
+    case ELEMENT_VERS_MISMATCH_WARN:
+        versionEmitted = doc->lexer->versionEmitted;
+        declared = doc->lexer->doctype;
+        version = versionEmitted == 0 ? declared : versionEmitted;
+        extra_string = TY_(HTMLVersionNameFromCode)(version, 0);
+        if (!extra_string)
+            extra_string = tidyLocalizedString(STRING_HTML_PROPRIETARY);
+        messageNode(doc, TidyWarning, code, node, fmt, nodedesc, extra_string);
+        break;
+
+    case ELEMENT_VERS_MISMATCH_ERROR:
+        versionEmitted = doc->lexer->versionEmitted;
+        declared = doc->lexer->doctype;
+        version = versionEmitted == 0 ? declared : versionEmitted;
+        extra_string = TY_(HTMLVersionNameFromCode)(version, 0);
+        if (!extra_string)
+            extra_string = tidyLocalizedString(STRING_HTML_PROPRIETARY);
+        messageNode(doc, TidyError, code, node, fmt, nodedesc, extra_string);
+        break;
+
     case MISSING_TITLE_ELEMENT:
     case INCONSISTENT_VERSION:
     case MALFORMED_DOCTYPE:
diff --git a/src/message.h b/src/message.h
index a519766..7c49499 100644
--- a/src/message.h
+++ b/src/message.h
@@ -98,6 +98,8 @@ typedef enum {
     CANT_BE_NESTED,
     OBSOLETE_ELEMENT,
     PROPRIETARY_ELEMENT,
+    ELEMENT_VERS_MISMATCH_ERROR,
+    ELEMENT_VERS_MISMATCH_WARN,
     UNKNOWN_ELEMENT,
     TRIM_EMPTY_ELEMENT,
     COERCE_TO_ENDTAG,
@@ -137,6 +139,8 @@ typedef enum {
     BAD_ATTRIBUTE_VALUE,
     UNEXPECTED_GT,
     PROPRIETARY_ATTRIBUTE,
+    MISMATCHED_ATTRIBUTE_ERROR,
+    MISMATCHED_ATTRIBUTE_WARN,
     PROPRIETARY_ATTR_VALUE,
     REPEATED_ATTRIBUTE,
     MISSING_IMAGEMAP,
@@ -168,8 +172,6 @@ typedef enum {
     WHITE_IN_URI,
 
     REMOVED_HTML5,                 /* this element removed from HTML5 */
-    BAD_BODY_HTML5,                /* attr on body removed from HTML5 */
-    BAD_ALIGN_HTML5,               /* use of align attr removed from HTML5 */
     BAD_SUMMARY_HTML5,             /* use of summary attr removed from HTML5 */
 
     PREVIOUS_LOCATION,             /* last */
diff --git a/src/tidylib.c b/src/tidylib.c
index 7e1e4bf..0dbdf05 100755
--- a/src/tidylib.c
+++ b/src/tidylib.c
@@ -1300,9 +1300,9 @@ void         tidyDocReportDoctype( TidyDocImpl* doc )
 }
 
 
-/* ######################################################################################
-   HTML5 STUFF
- */
+/*****************************************************************************
+ *  HTML5 STUFF
+ *****************************************************************************/
 #if !defined(NDEBUG) && defined(_MSC_VER)
 extern void show_not_html5(void);
 /* -----------------------------
@@ -1358,19 +1358,19 @@ Bool inRemovedInfo( uint tid )
     return no;
 }
 
-static Bool BadBody5( Node* node )
-{
-    if (TY_(AttrGetById)(node, TidyAttr_BACKGROUND) ||
-        TY_(AttrGetById)(node, TidyAttr_BGCOLOR)    ||
-        TY_(AttrGetById)(node, TidyAttr_TEXT)       ||
-        TY_(AttrGetById)(node, TidyAttr_LINK)       ||
-        TY_(AttrGetById)(node, TidyAttr_VLINK)      ||
-        TY_(AttrGetById)(node, TidyAttr_ALINK))
-    {
-        return yes;
-    }
-    return no;
-}
+/* Things that should not be in an HTML5 body. This is special for CheckHTML5(),
+ and we might just want to remove CheckHTML5()'s output altogether and count
+ on the default --strict-tags-attributes.
+ */
+static BadBody5Attribs[] = {
+    TidyAttr_BACKGROUND,
+    TidyAttr_BGCOLOR,
+    TidyAttr_TEXT,
+    TidyAttr_LINK,
+    TidyAttr_VLINK,
+    TidyAttr_ALINK,
+    TidyAttr_UNKNOWN /* Must be last! */
+};
 
 static Bool nodeHasAlignAttr( Node *node )
 {
@@ -1383,73 +1383,94 @@ static Bool nodeHasAlignAttr( Node *node )
     return no;
 }
 
-/* see http://www.whatwg.org/specs/web-apps/current-work/multipage/obsolete.html#obsolete */
-
+/*
+ *  Perform special checks for HTML, even when we're not using the default
+ *  option `--strict-tags-attributes yes`. This will ensure that HTML5 warning
+ *  and error output is given regardless of the new option, and ensure that
+ *  cleanup takes place. This provides mostly consistent Tidy behavior even with
+ *  the introduction of this new option. Note that strings have changed, though,
+ *  in order to maintain consistency with the `--strict-tags-attributes` 
+ *  messages.
+ *
+ *  See also: http://www.whatwg.org/specs/web-apps/current-work/multipage/obsolete.html#obsolete
+ */
 void TY_(CheckHTML5)( TidyDocImpl* doc, Node* node )
 {
-    /* Lexer* lexer = doc->lexer; */
     Bool clean = cfgBool( doc, TidyMakeClean );
+    Bool already_strict = cfgBool( doc, TidyStrictTagsAttr );
     Node* body = TY_(FindBody)( doc );
     Bool warn = yes;    /* should this be a warning, error, or report??? */
+    AttVal* attr = NULL;
+    int i = 0;
 #if !defined(NDEBUG) && defined(_MSC_VER)
-//    list_not_html5();
+    //    list_not_html5();
 #endif
     while (node)
     {
         if ( nodeHasAlignAttr( node ) ) {
-            /*\
-             * Is this for ALL elements that accept an 'align' attribute, or should
-             * this be a sub-set test
-            \*/
-            TY_(ReportWarning)(doc, node, node, BAD_ALIGN_HTML5);
+            /* @todo: Is this for ALL elements that accept an 'align' attribute,
+             * or should this be a sub-set test?
+             */
+
+            /* We will only emit this message if `--strict-tags-attributes==no`;
+             * otherwise if yes this message will be output during later
+             * checking.
+             */
+            if ( !already_strict )
+                TY_(ReportAttrError)(doc, node, TY_(AttrGetById)(node, TidyAttr_ALIGN), MISMATCHED_ATTRIBUTE_WARN);
         }
         if ( node == body ) {
-            if ( BadBody5(body) ) {
-                /* perhaps need a new/different warning for this, like
-                 * The background 'attribute" on the body element is obsolete. Use CSS instead.
-                 * but how to pass an attribute name to be embedded in the message.
-                \*/
-                TY_(ReportWarning)(doc, node, body, BAD_BODY_HTML5);
+            i = 0;
+            /* We will only emit these messages if `--strict-tags-attributes==no`;
+             * otherwise if yes these messages will be output during later
+             * checking.
+             */
+            if ( !already_strict ) {
+                while ( BadBody5Attribs[i] != TidyAttr_UNKNOWN ) {
+                    attr = TY_(AttrGetById)(node, BadBody5Attribs[i]);
+                    if ( attr )
+                        TY_(ReportAttrError)(doc, node, attr , MISMATCHED_ATTRIBUTE_WARN);
+                    i++;
+                }
             }
         } else
         if ( nodeIsACRONYM(node) ) {
             if (clean) {
-                /* replace with 'abbr' with warning to that effect 
-                 * maybe should use static void RenameElem( TidyDocImpl* doc, Node* node, TidyTagId tid )
+                /* Replace with 'abbr' with warning to that effect.
+                 * Maybe should use static void RenameElem( TidyDocImpl* doc, Node* node, TidyTagId tid )
                  */
                 TY_(CoerceNode)(doc, node, TidyTag_ABBR, warn, no);
             } else {
-                /* sadly, this stops writing of the tidied document, unless 'forced'
-                   TY_(ReportError)(doc, node, node, REMOVED_HTML5); 
-                   so go back to a 'warning' for now...
-                */
-                TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
+                if ( !already_strict )
+                    TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
             }
-        } else 
+        } else
         if ( nodeIsAPPLET(node) ) {
             if (clean) {
-                /* replace with 'object' with warning to that effect 
+                /* replace with 'object' with warning to that effect
                  * maybe should use static void RenameElem( TidyDocImpl* doc, Node* node, TidyTagId tid )
                  */
                 TY_(CoerceNode)(doc, node, TidyTag_OBJECT, warn, no);
             } else {
-                TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
+                if ( !already_strict )
+                    TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
             }
         } else
         if ( nodeIsBASEFONT(node) ) {
-            /*\ 
-             * basefont: CSS equivalen 'font-size', 'font-family' and 'color' on body or class on each subsequent element
-             * Difficult - If it is the first body element, then could consider adding that
-             *  to the <body> as a whole, else could perhaps apply it to all subsequent element.
-             *  But also in consideration is the fact that it was NOT supported in many browsers
-             *  For now just report a warning
-            \*/
+            /* basefont: CSS equivalent 'font-size', 'font-family' and 'color' 
+             * on body or class on each subsequent element.
+             * Difficult - If it is the first body element, then could consider
+             * adding that to the <body> as a whole, else could perhaps apply it
+             * to all subsequent elements. But also in consideration is the fact
+             * that it was NOT supported in many browsers.
+             * - For now just report a warning
+             */
+            if ( !already_strict )
                 TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
         } else
         if ( nodeIsBIG(node) ) {
-            /*\
-             * big: CSS equivalent 'font-size:larger'
-             * so could replace the <big> ... </big> with 
+            /* big: CSS equivalent 'font-size:larger'
+             * so could replace the <big> ... </big> with
              * <span style="font-size: larger"> ... </span>
              * then replace <big> with <span>
              * Need to think about that...
@@ -1461,94 +1482,185 @@ void TY_(CheckHTML5)( TidyDocImpl* doc, Node* node )
              * Also maybe need a specific message like
              * Element '%s' replaced with 'span' with a 'font-size: larger style attribute
              * maybe should use static void RenameElem( TidyDocImpl* doc, Node* node, TidyTagId tid )
-             *
-            \*/
+             */
             if (clean) {
                 TY_(AddStyleProperty)( doc, node, "font-size: larger" );
                 TY_(CoerceNode)(doc, node, TidyTag_SPAN, warn, no);
             } else {
-                TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
+                if ( !already_strict )
+                    TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
             }
         } else
         if ( nodeIsCENTER(node) ) {
-            /*\
-             * center: CSS equivalent 'text-align:center'
-             *  and 'margin-left:auto; margin-right:auto' on descendant blocks
-             * Tidy already handles this if 'clean' by SILENTLY generating the <style>
-             * and adding a <div class="c1"> around the elements.
+            /* center: CSS equivalent 'text-align:center'
+             * and 'margin-left:auto; margin-right:auto' on descendant blocks
+             * Tidy already handles this if 'clean' by SILENTLY generating the
+             * <style> and adding a <div class="c1"> around the elements.
              * see: static Bool Center2Div( TidyDocImpl* doc, Node *node, Node **pnode)
-            \*/
+             */
+            if ( !already_strict )
                 TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
-        } else 
+        } else
         if ( nodeIsDIR(node) ) {
-            /*\
-             *  dir: replace by <ul>
-             *  Tidy already actions this and issues a warning
-             *  Should this be CHANGED???
-            \*/
+            /* dir: replace by <ul>
+             * Tidy already actions this and issues a warning
+             * Should this be CHANGED???
+             */
+            if ( !already_strict )
                 TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
         } else
         if ( nodeIsFONT(node) ) {
-            /*\
-             * Tidy already handles this -
-             * If 'clean' replaced by CSS, else 
+            /* Tidy already handles this -
+             * If 'clean' replaced by CSS, else
              * if is NOT clean, and doctype html5 then warnings issued
              * done in Bool Font2Span( TidyDocImpl* doc, Node *node, Node **pnode ) (I think?)
-             *
-            \*/
+             */
+            if ( !already_strict )
                 TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
         } else
         if (( nodesIsFRAME(node) ) || ( nodeIsFRAMESET(node) ) || ( nodeIsNOFRAMES(node) )) {
-            /*\
-             * YOW: What to do here?????? Maybe <iframe>????
-            \*/
+            /* YOW: What to do here?????? Maybe <iframe>????
+             */
+            if ( !already_strict )
                 TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
         } else
         if ( nodeIsSTRIKE(node) ) {
-            /*\
-             * strike: CSS equivalent 'text-decoration:line-through'
+            /* strike: CSS equivalent 'text-decoration:line-through'
              * maybe should use static void RenameElem( TidyDocImpl* doc, Node* node, TidyTagId tid )
-            \*/
+             */
             if (clean) {
                 TY_(AddStyleProperty)( doc, node, "text-decoration: line-through" );
                 TY_(CoerceNode)(doc, node, TidyTag_SPAN, warn, no);
             } else {
-                TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
+                if ( !already_strict )
+                    TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
             }
         } else
         if ( nodeIsTT(node) ) {
-            /*\
-             * tt: CSS equivalent 'font-family:monospace'
+            /* tt: CSS equivalent 'font-family:monospace'
              * Tidy presently does nothing. Tidy5 issues a warning
              * But like the 'clean' <font> replacement this could also be replaced with CSS
              * maybe should use static void RenameElem( TidyDocImpl* doc, Node* node, TidyTagId tid )
-             *
-            \*/
+             */
             if (clean) {
                 TY_(AddStyleProperty)( doc, node, "font-family: monospace" );
                 TY_(CoerceNode)(doc, node, TidyTag_SPAN, warn, no);
             } else {
-                TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
+                if ( !already_strict )
+                    TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
             }
         } else
-        if (TY_(nodeIsElement)(node)) {
-            if (node->tag) {
-                if ((!(node->tag->versions & VERS_HTML5))||(inRemovedInfo(node->tag->id))) {
-                    /* issue warning for elements like 'markquee' */
-                    TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
+            if (TY_(nodeIsElement)(node)) {
+                if (node->tag) {
+                    if ((!(node->tag->versions & VERS_HTML5))||(inRemovedInfo(node->tag->id))) {
+                        if ( !already_strict )
+                            TY_(ReportWarning)(doc, node, node, REMOVED_HTML5);
+                    }
+                }
+            }
+
+        if (node->content)
+            TY_(CheckHTML5)( doc, node->content );
+        
+        node = node->next;
+    }
+}
+/*****************************************************************************
+ *  END HTML5 STUFF
+ *****************************************************************************/
+
+
+/*
+ * Check and report HTML tags and attributes that are:
+ *  - Proprietary, and/or
+ *  - Not supported in the current version of HTML, defined as the version
+ *    of HTML that we are emitting.
+ * Proprietary items are reported as WARNINGS, and version mismatches will
+ * be reported as WARNING or ERROR in the following conditions:
+ *  - ERROR if the emitted doctype is a strict doctype.
+ *  - WARNING if the emitted doctype is a non-strict doctype.
+ * The propriety checks are *always* run as they have always been an integral
+ * part of Tidy. The version checks are controlled by `strict-tags-attributes`.
+ */
+void TY_(CheckHTMLTagsAttribsVersions)( TidyDocImpl* doc, Node* node )
+{
+    uint versionEmitted = doc->lexer->versionEmitted;
+    uint declared = doc->lexer->doctype;
+    uint version = versionEmitted == 0 ? declared : versionEmitted;
+    int tagReportType = VERS_STRICT & version ? ELEMENT_VERS_MISMATCH_ERROR : ELEMENT_VERS_MISMATCH_WARN;
+    int attrReportType = VERS_STRICT & version ? MISMATCHED_ATTRIBUTE_ERROR : MISMATCHED_ATTRIBUTE_WARN;
+    Bool check_versions = cfgBool( doc, TidyStrictTagsAttr );
+    AttVal *next_attr, *attval;
+    Bool attrIsProprietary = no;
+    Bool attrIsMismatched = yes;
+
+    while (node)
+    {
+        /* This bit here handles our HTML tags */
+        if ( TY_(nodeIsElement)(node) && node->tag ) {
+
+            /* Leave XML stuff alone. */
+            if ( !cfgBool(doc, TidyXmlTags) )
+            {
+                /* Version mismatches take priority. */
+                if ( check_versions && !(node->tag->versions & version) )
+                {
+                    TY_(ReportError)(doc, NULL, node, tagReportType );
+                }
+                /* If it's not mismatched, it could still be proprietary. */
+                else if ( node->tag->versions & VERS_PROPRIETARY )
+                {
+                    if ( !cfgBool(doc, TidyMakeClean) ||
+                        ( !nodeIsNOBR(node) && !nodeIsWBR(node) ) )
+                    {
+                        TY_(ReportError)(doc, NULL, node, PROPRIETARY_ELEMENT );
+
+                        if ( nodeIsLAYER(node) )
+                            doc->badLayout |= USING_LAYER;
+                        else if ( nodeIsSPACER(node) )
+                            doc->badLayout |= USING_SPACER;
+                        else if ( nodeIsNOBR(node) )
+                            doc->badLayout |= USING_NOBR;
+                    }
                 }
             }
         }
 
-        if (node->content)
-            TY_(CheckHTML5)( doc, node->content );
+        /* And this bit here handles our attributes */
+        if (TY_(nodeIsElement)(node))
+        {
+            attval = node->attributes;
 
+            while (attval)
+            {
+                next_attr = attval->next;
+
+                attrIsProprietary = TY_(AttributeIsProprietary)(node, attval);
+                attrIsMismatched = check_versions ? TY_(AttributeIsMismatched)(node, attval, doc) : no;
+                /* Let the PROPRIETARY_ATTRIBUTE warning have precedence. */
+                if ( attrIsProprietary )
+                    TY_(ReportAttrError)(doc, node, attval, PROPRIETARY_ATTRIBUTE);
+                else if ( attrIsMismatched )
+                {
+                    TY_(ReportAttrError)(doc, node, attval, attrReportType);
+                }
+
+                /* @todo: do we need a new option to drop mismatches? Or should we
+                 simply drop them? */
+                if ( ( attrIsProprietary || attrIsMismatched ) && cfgBool(doc, TidyDropPropAttrs) )
+                    TY_(RemoveAttribute)( doc, node, attval );
+
+                attval = next_attr;
+            }
+        }
+
+        if (node->content)
+            TY_(CheckHTMLTagsAttribsVersions)( doc, node->content );
+        
         node = node->next;
     }
 }
-/* END HTML5 STUFF
-   ######################################################################################
- */
+
 
 #if !defined(NDEBUG) && defined(_MSC_VER)
 /* *** FOR DEBUG ONLY *** */
@@ -1686,7 +1798,6 @@ int         tidyDocCleanAndRepair( TidyDocImpl* doc )
     Bool tidyXmlTags = cfgBool( doc, TidyXmlTags );
     Bool wantNameAttr = cfgBool( doc, TidyAnchorAsName );
     Bool mergeEmphasis = cfgBool( doc, TidyMergeEmphasis );
-    ctmbstr sdef = NULL;
     Node* node;
 
 #if !defined(NDEBUG) && defined(_MSC_VER)
@@ -1747,12 +1858,7 @@ int         tidyDocCleanAndRepair( TidyDocImpl* doc )
 
     /* remember given doctype for reporting */
     node = TY_(FindDocType)(doc);
-    sdef = tidyOptGetValue((TidyDoc)doc, TidyDoctype );
-    if (!sdef)
-        sdef = tidyOptGetCurrPick((TidyDoc) doc, TidyDoctypeMode );
-    if (sdef && (strcmp(sdef,"html5") == 0)) {
-        TY_(CheckHTML5)( doc, &doc->root );
-    }
+
     if (node)
     {
         AttVal* fpi = TY_(GetAttrByName)(node, "PUBLIC");
@@ -1798,6 +1904,14 @@ int         tidyDocCleanAndRepair( TidyDocImpl* doc )
     if ( xmlOut && xmlDecl )
         TY_(FixXmlDecl)( doc );
 
+    /* At this point the apparent doctype is going to be as stable as
+       it can ever be, so we can start detecting things that shouldn't
+       be in this version of HTML
+     */
+    if (doc->lexer->versionEmitted & VERS_HTML5)
+         TY_(CheckHTML5)( doc, &doc->root );
+    TY_(CheckHTMLTagsAttribsVersions)( doc, &doc->root );
+
 #if !defined(NDEBUG) && defined(_MSC_VER)
     SPRTF("All nodes AFTER clean and repair\n");
     dbg_show_all_nodes( doc, &doc->root, 0  );
diff --git a/version.txt b/version.txt
index eac687d..79420fa 100644
--- a/version.txt
+++ b/version.txt
@@ -1,2 +1,2 @@
-5.1.36_attr_phase1
+5.1.36_attr_phase2
 2016.02.12