Fix mismatched PHP close tag inside string in XML source (#1656)

* Fix mismatched PHP close tag inside string in XML

* Fix dropping out of PHP sublanguage inside XML

* Fix ghost XML strings for each string in PHP block

* Simplify PHP string skipping for XML source

* Fix PHP strings backslash escape inside XML

src/languages/xml.js

@@ -60,7 +60,15 @@ function(hljs) {
       {
         begin: /<\?(php)?/, end: /\?>/,
         subLanguage: 'php',
-        contains: [{begin: '/\\*', end: '\\*/', skip: true}]
+        contains: [
+          // We don't want the php closing tag ?> to close the PHP block when
+          // inside any of the following blocks:
+          {begin: '/\\*', end: '\\*/', skip: true},
+          {begin: 'b"', end: '"', skip: true},
+          {begin: 'b\'', end: '\'', skip: true},
+          hljs.inherit(hljs.APOS_STRING_MODE, {illegal: null, className: null, contains: null, skip: true}),
+          hljs.inherit(hljs.QUOTE_STRING_MODE, {illegal: null, className: null, contains: null, skip: true})
+        ]
       },
       {
         className: 'tag',