Implement skip: true

The new property allows crude parsing within sub-languages to parse
out the whole buffer before actually running processBuffer().

Author: isagalaev

docs/reference.rst

@@ -296,3 +296,32 @@ The value of the attribute controls which language or languages will be used for
 * language name: explicit highlighting with the specified language
 * empty array: auto detection with all the languages available
 * array of language names: auto detection constrained to the specified set
+
+skip
+^^^^
+
+**type**: boolean
+
+Skips any markup processing for the mode ensuring that it remains a part of its
+parent buffer along with the starting and the ending lexemes. This works in
+conjunction with the parent's :ref:`subLanguage` when it requires complex
+parsing.
+
+Consider parsing JSX inside JavaScript::
+
+  var x = <node> text <child/> text </node>;
+
+You have to correctly balance opening and ending angle brackets to make sure
+that the entire XML node is parsed out before it can be highlighted with a
+sub-language::
+
+  {
+    begin: /</, end: />/,
+    subLanguague: 'xml',
+    contains: [
+      {begin: /</, end: />/, skip: true, contains: ['self']}
+    ]
+  }
+
+Without ``skip: true`` every angle bracket within the root node would cause the
+parser to drop out back into JavaScript.

src/highlight.js

@@ -393,12 +393,16 @@ https://highlightjs.org/
 
       var new_mode = subMode(lexeme, top);
       if (new_mode) {
-        if (new_mode.excludeBegin) {
+        if (new_mode.skip) {
           mode_buffer += lexeme;
-        }
-        processBuffer();
-        if (!new_mode.returnBegin && !new_mode.excludeBegin) {
-          mode_buffer = lexeme;
+        } else {
+          if (new_mode.excludeBegin) {
+            mode_buffer += lexeme;
+          }
+          processBuffer();
+          if (!new_mode.returnBegin && !new_mode.excludeBegin) {
+            mode_buffer = lexeme;
+          }
         }
         startNewMode(new_mode, lexeme);
         return new_mode.returnBegin ? 0 : lexeme.length;
@@ -407,18 +411,24 @@ https://highlightjs.org/
       var end_mode = endOfMode(top, lexeme);
       if (end_mode) {
         var origin = top;
-        if (!(origin.returnEnd || origin.excludeEnd)) {
+        if (origin.skip) {
           mode_buffer += lexeme;
-        }
-        processBuffer();
-        if (origin.excludeEnd) {
-          mode_buffer = lexeme;
+        } else {
+          if (!(origin.returnEnd || origin.excludeEnd)) {
+            mode_buffer += lexeme;
+          }
+          processBuffer();
+          if (origin.excludeEnd) {
+            mode_buffer = lexeme;
+          }
         }
         do {
           if (top.className) {
             result += '</span>';
           }
-          relevance += top.relevance;
+          if (!top.skip) {
+            relevance += top.relevance;
+          }
           top = top.parent;
         } while (top != end_mode.parent);
         if (end_mode.starts) {