Add support for link 'as' attribute (closes #449)

include/tidyenum.h

@@ -848,6 +848,8 @@ typedef enum
 
   TidyAttr_INTEGRITY,         /**< INTEGRITY= */
 
+  TidyAttr_AS,               /**< AS= */
+
   N_TIDY_ATTRIBS              /**< Must be last */
 } TidyAttrId;
 

src/attrdict.c

@@ -1950,6 +1950,7 @@ const AttrVersion TY_(W3CAttrsFor_LINK)[] =
 {
   INCLUDE_ARIA
   INCLUDE_MICRODATA
+  { TidyAttr_AS,                    xxxx|xxxx|xxxx|xxxx|xxxx|xxxx|xxxx|xxxx|xxxx|xxxx|xxxx|xxxx|xxxx|HT50|XH50 },
   { TidyAttr_CHARSET,               xxxx|xxxx|H40T|H41T|X10T|H40F|H41F|X10F|H40S|H41S|X10S|XH11|XB10|xxxx|xxxx },
   { TidyAttr_CLASS,                 xxxx|xxxx|H40T|H41T|X10T|H40F|H41F|X10F|H40S|H41S|X10S|XH11|XB10|HT50|XH50 }, /* CORE override */
   { TidyAttr_CROSSORIGIN,           xxxx|xxxx|xxxx|xxxx|xxxx|xxxx|xxxx|xxxx|xxxx|xxxx|xxxx|xxxx|xxxx|HT50|XH50 },

src/attrs.c

@@ -440,6 +440,9 @@ static const Attribute attribute_defs [] =
 
   { TidyAttr_INTEGRITY,                "integrity",              CH_PCDATA   },
 
+  /* Preload spec: https://www.w3.org/TR/preload/ */
+  { TidyAttr_AS,                       "as",                     CH_PCDATA   },
+
   /* this must be the final entry */
   { N_TIDY_ATTRIBS,                    NULL,                     NULL         }
 };